Address inconsistent-return-statements

Pylint warns about inconsistent return statements when some paths of a
function return None implicitly. Make all implicit returns either
explicit or raise a proper exception.

See: https://pagure.io/freeipa/issue/7758
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipatests/test_cmdline/test_help.py

@@ -66,6 +66,8 @@ class CLITestContext:
                 return False
             self.exception = exc_value
             return True
+        else:
+            return None
 
 
 def test_ipa_help():