Rucio breaks DIRAC run
Motivation
----------
After the 1.27.0rc1 release, the DIRAC runs are throwing an error produced by Rucio. The cause is a missing `rucio.cfg` file. The `is_client` function thus throws the following error:
```
2021-11-25T05:03:46.4056355Z �[1m�[31mE               RuntimeError: Could not load Rucio configuration file. Rucio looked in the following paths for a configuration file, in order:�[0m
2021-11-25T05:03:46.4057329Z �[1m�[31mE               	/opt/rucio/etc/rucio.cfg�[0m
```

https://github.com/rucio/rucio/blob/b820877f58c975740d9ea1fd448c3dcf2eb013cf/lib/rucio/common/utils.py#L1560-L1579


Issue: DIRACGrid/DIRAC#5637

Modification
------------
@bari12 suggested that the `is_client` function should return `True` in case of a missing configuration file.
diff --git a/lib/rucio/common/utils.py b/lib/rucio/common/utils.py
index ce254ea12..06fef1841 100644
--- a/lib/rucio/common/utils.py
+++ b/lib/rucio/common/utils.py
@@ -1564,12 +1564,16 @@ def is_client():
     :returns client_mode: True if is called from a client, False if it is called from a server/daemon
     """
     if 'RUCIO_CLIENT_MODE' not in os.environ:
-        if config_has_section('database'):
-            client_mode = False
-        elif config_has_section('client'):
+        try:
+            if config_has_section('database'):
+                client_mode = False
+            elif config_has_section('client'):
+                client_mode = True
+            else:
+                client_mode = False
+        except RuntimeError:
+            # If no configuration file is found the default value should be True
             client_mode = True
-        else:
-            client_mode = False
     else:
         if os.environ['RUCIO_CLIENT_MODE']:
             client_mode = True
['lib/rucio/common/utils.py']