Navigage Buildkite builds with more nuance
- If we want to fetch a tag, Buildkite needs it as a "branch" (this means more like "ref to fetch").
- The API gets upset if we pass "refs/tags/...", so just pass the tag name without the prefix, which works.
- Do a better job with commits and pass a real branch to fetch.
- Built a commit with Buildkite.
- Build a revision with Buildkite.
Reviewed By: chad
Maniphest Tasks: T12173
Differential Revision: https://secure.phabricator.com/D17282