Ignore remote errors in parsing Mercurial log

Summary:
This probably indicates some none fatal error, e.g.:

> remote: Certificate invalid: name is not a listed principal

The best thing here would be to avoid the error but we shouldn't explode even if it is there.
I tried to mute the error from the output but didn't find a switch or config option to do it.

Test Plan:
  $ hg outgoing --branch default --style default

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5267