Have .unir.yml have a keyword that automatically disqualifies a PR from being merged.

If / when a green commit status is shown, unir should do a check to see if an agreement to merge has been made it should merge the PR accordingly.

Docs on Status for Github's API can be found here: https://developer.github.com/v3/repos/statuses/

Example:

.unir.yml

whitelist:
  - docker/release-engineering
  - kubernetes/maintainers
  - my_org/my-team

Any members of those teams should be able to approve pull requests in that repository regardless if they repository is actually owned by those teams.

Implementation ideas:

This can be implemented by adding an expanding teams to all members when doing the whitelist check and then caching those teams with a TTL so that we don't have to do that check every time (although it probably won't be that expensive to do that).

Since github usernames cannot contain anything outside of alphanumeric characters and hyphens we can only expand whitelist members that contain a slash character

With the inclusion of #12 we should not have commit statuses trigger a successful merge scenario since this would cause a double merge scenario as seen in:

unir_1   | time="2018-04-02T22:11:16Z" level=info msg="Agreement reached! Merging https://github.com/seemethere/unir/pull/13"
unir_1   | time="2018-04-02T22:11:17Z" level=info msg="Merge successful for https://github.com/seemethere/unir/pull/13"
unir_1   | time="2018-04-02T22:11:18Z" level=info msg="Agreement reached! Merging https://github.com/seemethere/unir/pull/13"
unir_1   | time="2018-04-02T22:11:19Z" level=error msg="Merge failed for https://github.com/seemethere/unir/pull/13: , PUT https://api.github.com/repos/seemethere/unir/pulls/13/merge: 405 Pull Request is not mergeable []"