Replaced bare except

According to H201 [1], we shouldn't use bare except,
use 'except Exception:' at least. In this patchset, it is
fixed.

[1]: http://docs.openstack.org/developer/hacking/

Change-Id: Id64712dba67db53a7c20ef38b56c20cebcd63821

barbicanclient/base.py

@@ -39,7 +39,7 @@ def validate_ref(ref, entity):
     try:
         _, entity_uuid = ref.rstrip('/').rsplit('/', 1)
         uuid.UUID(entity_uuid)
-    except:
+    except Exception:
         raise ValueError('{0} incorrectly specified.'.format(entity))
 
     return True