Use except x as y instead of except x, y

According to https://docs.python.org/3/howto/pyporting.html the
syntax changed in Python 3.x. The new syntax is usable with
Python >= 2.6 and should be preferred to be compatible with Python3.

Enabled hacking check H231.

Change-Id: I4c20a04bc7732efc2d4bbcbc3d285107b244e5fa

log_processor/worker.py

@@ -180,7 +180,7 @@ class LogRetriever(threading.Thread):
         raw_buf = b''
         try:
             gzipped, raw_buf = self._get_log_data(source_url, retry)
-        except urllib2.HTTPError, e:
+        except urllib2.HTTPError as e:
             if e.code == 404:
                 logging.info("Unable to retrieve %s: HTTP error 404" %
                              source_url)