Fix error handling when pushing to branch

[JakeQuilty]

When the script was running, one of the repos in the list that it tried to push to was archived. That made the whole script stop running with an error. I think this could be fixed by adding some error handling in git-manager.py around the bash commands. We should have it log and print out a list of the repos that failed.

• Handle pushing to archived repo
• Handle pushing to repo that already has a branch with the same name
• Handle pushing to repo that your token doesn't have contributor access to
• Handle other things

[AndrewCopeland]

Maybe have a configuration attribute called continue_on_failure: yes that will continue if failed and will push to a default failure file that can also be provided like continue_on_failure_file: /file/path/to/failures.log.