Fix instance_update() passing SQLA objects to send_update()

In a previous commit, the notifications plumbing was made to expect an
instance object in some places. The legacy instance_update() method was
still passing DB objects to that method, causing a failure to actually
emit the notification.

Change-Id: Idafed020668f013182fab5c3f6829aedf20edaed
Closes-Bug: #1396324
Merge "Fix instance_update() passing SQLA objects to send_update()"