git cl believes I'm working inside GCE

Looks like the error codes issued by python's http library might vary
between versions/distros. The code tries to reach an URL which is only valid
inside GCE and in the event of getting an error it assumes the user is
a non-googler.

At least in this case, we're seeing:

  third_party.httplib2.socks.HTTPError: (404, 'No such domain')

Adding this exception type allows the function to work correctly.

Change-Id: I08d3656b25d9046f8b2fc0da2a2b7c7a698c1d92
Reviewed-on: https://chromium-review.googlesource.com/978212
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>

gerrit_util.py

@@ -256,7 +256,8 @@ class GceAuthenticator(Authenticator):
     # Based on https://cloud.google.com/compute/docs/metadata#runninggce
     try:
       resp, _ = cls._get(cls._INFO_URL)
-    except (socket.error, httplib2.ServerNotFoundError):
+    except (socket.error, httplib2.ServerNotFoundError,
+            httplib2.socks.HTTPError):
       # Could not resolve URL.
       return False
     return resp.get('metadata-flavor') == 'Google'