MSUnmerged: Reduce printouts for known exceptions.
**Impact of the bug**
MSUnmerged

**Describe the bug**
Not exactly a bug. While looking into the logs from MSUnmerged I found that  plenty of the properly handled exceptions who inherit from WMCoreException are printing also an unneeded back trace which clutters  the logs. This is especially valid for exceptions which are used for signaling some kind of an event inside the script such as pipeline exit etc. [1] [2]

**How to reproduce it**
look into the logs 

**Expected behavior**
Cleaner logging messages for handled exceptions.
 
**Additional context and error message**
[1]
```
2021-07-23 00:00:15,483:INFO:MSUnmerged: RSE: T2_US_Wisconsin With old consistency record in Rucio Consistency Monitor. Skipping it in the current run.
2021-07-23 00:00:15,485:ERROR:MSUnmerged: plineUnmerged: Run on RSE: T2_US_Wisconsin was interrupted due to: MSUnmergedException: MSUnmergedPlineExit: RSE: %s With old consistency record in Rucio Consistency Monitor. Skipping it in the c
urrent run.. 
Will retry again in the next cycle.
Traceback (most recent call last):
  File "/data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/WMCore/MicroService/MSUnmerged/MSUnmerged.py", line 205, in _execute
    pline.run(MSUnmergedRSE(rseName))
  File "/data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/Utils/Pipeline.py", line 140, in run
    return reduce(lambda obj, functor: functor(obj), self.funcLine, obj)
  File "/data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/Utils/Pipeline.py", line 140, in <lambda>
    return reduce(lambda obj, functor: functor(obj), self.funcLine, obj)
  File "/data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/Utils/Pipeline.py", line 72, in __call__
    return self.run(obj)
  File "/data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/Utils/Pipeline.py", line 75, in run
    return self.func(obj, *self.args, **self.kwargs)
  File "/data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/WMCore/MicroService/MSUnmerged/MSUnmerged.py", line 372, in consRecordAge
    raise MSUnmergedPlineExit(msg)
WMCore.MicroService.MSUnmerged.MSUnmerged.MSUnmergedPlineExit: <@========== WMException Start ==========@>
Exception Class: MSUnmergedPlineExit
Message: MSUnmergedException: MSUnmergedPlineExit: RSE: %s With old consistency record in Rucio Consistency Monitor. Skipping it in the current run.
        ClassName : None
        ModuleName : WMCore.MicroService.MSUnmerged.MSUnmerged
        MethodName : __init__
        ClassInstance : None
        FileName : /data/srv/HG2108c/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre2/lib/python3.8/site-packages/WMCore/MicroService/MSUnmerged/MSUnmerged.py
        LineNumber : 46
        ErrorNr : 0

Traceback: 

<@---------- WMException End ----------@>

```

[2]
```
2021-07-23 10:49:47,941:INFO:MSUnmerged: RSE: T2_US_Nebraska In non-final state in Rucio Consistency Monitor. Skipping it in the current run.
2021-07-23 10:49:48,068:ERROR:MSUnmerged: plineUnmerged: Run on RSE: T2_US_Nebraska was interrupted due to: MSUnmergedException: MSUnmergedPlineExit: RSE: %s In non-final state in Rucio Cons
Will retry again in the next cycle.
Traceback (most recent call last):
  File "/data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/WMCore/MicroService/MSUnmerged/MSUnmerged.py", line 205, in _execute
    pline.run(MSUnmergedRSE(rseName))
  File "/data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/Utils/Pipeline.py", line 140, in run
    return reduce(lambda obj, functor: functor(obj), self.funcLine, obj)
  File "/data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/Utils/Pipeline.py", line 140, in <lambda>
    return reduce(lambda obj, functor: functor(obj), self.funcLine, obj)
  File "/data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/Utils/Pipeline.py", line 72, in __call__
    return self.run(obj)
  File "/data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/Utils/Pipeline.py", line 75, in run
    return self.func(obj, *self.args, **self.kwargs)
  File "/data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/WMCore/MicroService/MSUnmerged/MSUnmerged.py", line 376, in consRecordAge
    raise MSUnmergedPlineExit(msg)
WMCore.MicroService.MSUnmerged.MSUnmerged.MSUnmergedPlineExit: <@========== WMException Start ==========@>
Exception Class: MSUnmergedPlineExit
Message: MSUnmergedException: MSUnmergedPlineExit: RSE: %s In non-final state in Rucio Consistency Monitor. Skipping it in the current run.
        ClassName : None
        ModuleName : WMCore.MicroService.MSUnmerged.MSUnmerged
        MethodName : __init__
        ClassInstance : None
        FileName : /data/srv/HG2108d/sw/slc7_amd64_gcc630/cms/reqmgr2ms/0.5.1.pre3/lib/python3.8/site-packages/WMCore/MicroService/MSUnmerged/MSUnmerged.py
        LineNumber : 46
        ErrorNr : 0

Traceback: 

<@---------- WMException End ----------@>
```
diff --git a/src/python/WMCore/MicroService/MSUnmerged/MSUnmerged.py b/src/python/WMCore/MicroService/MSUnmerged/MSUnmerged.py
index 235984c9a..c1b6173cb 100644
--- a/src/python/WMCore/MicroService/MSUnmerged/MSUnmerged.py
+++ b/src/python/WMCore/MicroService/MSUnmerged/MSUnmerged.py
@@ -209,13 +209,13 @@ class MSUnmerged(MSCore):
                     self.logger.info(msg, pline.name, rseName)
                     continue
             except MSUnmergedPlineExit as ex:
-                msg = "%s: Run on RSE: %s was interrupted due to: %s. "
-                msg += "\\nWill retry again in the next cycle."
-                self.logger.exception(msg, pline.name, rseName, ex.message)
+                msg = "%s: Run on RSE: %s was interrupted due to: %s "
+                msg += "Will retry again in the next cycle."
+                self.logger.warning(msg, pline.name, rseName, ex.message)
                 continue
             except Exception as ex:
-                msg = "%s: General error from pipeline. RSE: %s. Error:  \\n%s."
-                msg += "\\nWill retry again in the next cycle."
+                msg = "%s: General error from pipeline. RSE: %s. Error: %s "
+                msg += "Will retry again in the next cycle."
                 self.logger.exception(msg, pline.name, rseName, str(ex))
                 continue
         return self.plineCounters[pline.name]['totalNumRses'], \\
@@ -236,8 +236,9 @@ class MSUnmerged(MSCore):
             ctx = gfal2.creat_context()
             gfal2.set_verbose(gfal2.verbose_level.names[self.msConfig['gfalLogLevel']])
         except Exception as ex:
-            msg = "RSE: %s, Failed to create gfal2 Context object. Skipping it in the current run."
-            self.logger.info(msg, rse['name'])
+            msg = "RSE: %s, Failed to create gfal2 Context object. " % rse['name']
+            msg += "Skipping it in the current run."
+            self.logger.exception(msg)
             raise MSUnmergedPlineExit(msg)
 
         # Start cleaning one directory at a time:
@@ -292,9 +293,9 @@ class MSUnmerged(MSCore):
                             msg = "RSE: %s Failed to purge nonEmpty directory: %s"
                             self.logger.error(msg, rse['name'], dirPfn)
                     except Exception as ex:
-                        msg = "Error while cleaning RSE: %s"
+                        msg = "Error while cleaning RSE: %s. "
                         msg += "Will retry in the next cycle. Err: %s"
-                        self.logger.debug(msg, rse['name'], str(ex))
+                        self.logger.warning(msg, rse['name'], str(ex))
         rse['isClean'] = self._checkClean(rse)
 
         return rse
@@ -362,21 +363,31 @@ class MSUnmerged(MSCore):
         :return:    rse or raises MSUnmergedPlineExit
         """
         rseName = rse['name']
+
+        if rseName not in self.rseConsStats:
+            msg = "RSE: %s Missing in stats records at Rucio Consistency Monitor. " % rseName
+            msg += "Skipping it in the current run."
+            self.logger.warning(msg)
+            raise MSUnmergedPlineExit(msg)
+
         isConsDone = self.rseConsStats[rseName]['status'] == 'done'
         isConsNewer = self.rseConsStats[rseName]['end_time'] > self.rseTimestamps[rseName]['prevStartTime']
         isRootFailed = self.rseConsStats[rseName]['root_failed']
 
         if not isConsNewer:
-            msg = "RSE: %s With old consistency record in Rucio Consistency Monitor. Skipping it in the current run."
-            self.logger.info(msg, rseName)
+            msg = "RSE: %s With old consistency record in Rucio Consistency Monitor. " % rseName
+            msg += "Skipping it in the current run."
+            self.logger.info(msg)
             raise MSUnmergedPlineExit(msg)
         if not isConsDone:
-            msg = "RSE: %s In non-final state in Rucio Consistency Monitor. Skipping it in the current run."
-            self.logger.info(msg, rseName)
+            msg = "RSE: %s In non-final state in Rucio Consistency Monitor. " % rseName
+            msg += "Skipping it in the current run."
+            self.logger.warning(msg)
             raise MSUnmergedPlineExit(msg)
         if isRootFailed:
-            msg = "RSE: %s With failed root in Rucio Consistency Monitor. Skipping it in the current run."
-            self.logger.info(msg, rseName)
+            msg = "RSE: %s With failed root in Rucio Consistency Monitor. " % rseName
+            msg += "Skipping it in the current run."
+            self.logger.warning(msg)
             raise MSUnmergedPlineExit(msg)
 
         return rse
@@ -492,7 +503,7 @@ class MSUnmerged(MSCore):
         already recorded in the RSE in order to resolve the lfn to pfn mapping
         and then tries to parse the resultant pfn and cut off the lfn part.
         :param rse: The RSE to be checked
-        :return:    rse or raises MSUnmergedPlineExit
+        :return:    rse
         """
         # NOTE:  pfnPrefix here is considered the full part of the pfn up to the
         #        beginning of the lfn part rather than just the protocol prefix
['src/python/WMCore/MicroService/MSUnmerged/MSUnmerged.py']