since cros_mark_as_stable makes git commits, it should log the resulting git info for each commit.  this helps coordinate log info in buildbot logs as to where a specific git sha1 is coming from.

we do this to a degree already with the CommitQueueSync stage because the patch apply/cherry-picking logic includes it.  example output there:
[patch_branch d8060e80b] Fix fscap policy for NYC Arc.
 Author: khmel <khmel@google.com>
 Date: Mon Dec 5 14:20:50 2016 -0800
 1 file changed, 1 insertion(+)

we probably even want something a bit more verbose in our logging like including the commit timestamp too (and not just the author timestamp)