maintner: better gerrit commit syncing

Don't update Gerrit refs until after corresponding git commit
mutations are added and processed. Do the batching earlier, so we
always make forward progress.

Also better logging so you can see what's happening.

Change-Id: I493071af7bccec5abf156025389376b9fc182dc8
Reviewed-on: https://go-review.googlesource.com/38672
Reviewed-by: Kevin Burke <kev@inburke.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
3 files changed