CQ: handle more error conditions in try_job_on_rietveld.py

This catches errors I observed running local CQ instance.
All errors are temporary network/service hiccups
and so are caught and logged as warnings.

BUG=none

Review URL: https://codereview.chromium.org/33443003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/commit-queue@230786 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed