Ensure default commit with --prod is HEAD

Change-Id: I64b694560fac1a27f5b9832d63faa7f0e72264f2
Ensure the commit resolved locally rather than remotely

This would be a problem if deploying HEAD on a branch on the local repo, since
the remote server only uses the master branch which likely has a different HEAD.

Change-Id: I45f07b2fded010f8e5456e62010c3bf9fb79c548