Create upstream patches for additions to `buildbot`

[MagicRB]

This is a tracking issue for the upstreaming of certain overrides and "hacks" we currently have in place, a (hopefully) exhaustive list follows:

• [ ] GitHubAppStatusPush
• [ ] AvatarGitHub
• [x] GitHub retries as suggested in #178

[zowoq]

Looks like all the patches have been upstreamed?