[py2py3] Python3 list sort built-in takes no positional arguments
**Impact of the bug**
WMCore in general

**Describe the bug**
Another popular issue while integrating python3 unit tests in our jenkins CI.
Python3 list `sort` built-in does not take any positional arguments, where many of our MySQL bind handling fails, see [1]

**How to reproduce it**
Run the DBSBufferFile unit test provided in the details

**Expected behavior**
List sorting functionality should remain intact and work in both python2 and python3 :-D

**Additional context and error message**
Documentation: https://docs.python.org/3.8/library/stdtypes.html#list.sort

[1]
```
======================================================================
ERROR: _testProperties_
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/dmwm/wmcore_unittest/WMCore/test/python/WMComponent_t/DBS3Buffer_t/DBSBufferFile_t.py", line 41, in setUp
    locationAction.execute(siteName="se1.cern.ch")
  File "/home/dmwm/wmcore_unittest/WMCore/src/python/WMComponent/DBS3Buffer/MySQL/DBSBufferFiles/AddLocation.py", line 23, in execute
    self.dbi.processData(self.sql, binds, conn = conn,
  File "/home/dmwm/wmcore_unittest/WMCore/src/python/WMCore/Database/DBCore.py", line 172, in processData
    r = self.executebinds(s, b, connection=connection,
  File "/home/dmwm/wmcore_unittest/WMCore/src/python/WMCore/Database/MySQLCore.py", line 126, in executebinds
    s, b = self.substitute(s, b)
  File "/home/dmwm/wmcore_unittest/WMCore/src/python/WMCore/Database/MySQLCore.py", line 77, in substitute
    bindVarNames.sort(stringLengthCompare)
TypeError: sort() takes no positional arguments
-------------------- >> begin captured logging << --------------------
root: DEBUG: Tables for WMComponent.DBS3Buffer created
--------------------- >> end captured logging << ---------------------
```
diff --git a/src/python/WMCore/REST/Server.py b/src/python/WMCore/REST/Server.py
index e7e856fa2..f9f12a1ab 100644
--- a/src/python/WMCore/REST/Server.py
+++ b/src/python/WMCore/REST/Server.py
@@ -188,7 +188,7 @@ class RESTFrontPage(object):
         if instances:
             instances = [dict(id=k, title=v[".title"], order=v[".order"])
                          for k, v in viewitems(instances())]
-            instances.sort(lambda a, b: a["order"] - b["order"])
+            instances.sort(key=lambda x: x["order"])
             self._preamble += (", REST_INSTANCES = %s" % json.dumps(instances))
 
         self._preamble += ";\\n%s" % (preamble or "")
['src/python/WMCore/REST/Server.py']