Record who submitted a change in the change message

If the change is successfully submitted and we know who the
submitter was (based on the most recent ChangeApproval), log
the submit event message from that user, rather than from the
"Gerrit Code Review" generic identity.

Bug: GERRIT-77
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed