GitLab

1. Add retry to http_client.
2. Make Findit more robust for unrecognized chromium revision.
3. Workaround a harmless bug in python 2.7
4. Give a better error message for check failure.

NOTRY=true

Review URL: https://codereview.chromium.org/538383002

Cr-Commit-Position: refs/heads/master@{#293528}