Improve Python 3.x compatibility

Per (proposed) Hacking H203 check, use the
non-deprecated except x as y: construct, which
works with any Python version >= 2.6

Change-Id: I42935ada01ea7487d76040832578e06ac8ad87dd

ceilometer/nova_client.py

@@ -31,7 +31,7 @@ def logged(func):
     def with_logging(*args, **kwargs):
         try:
             return func(*args, **kwargs)
-        except Exception, e:
+        except Exception as e:
             LOG.exception(e)
             raise