Add return of updated object on update from DB

There are a number of update methods in db/sqla/api
that update objects but no longer return the updated
reference for said object.

This patch adds the missing returns which are already
expected in the calling cidner/db/api wrapper. At some
point a close look at usage in callers
(ie cinder/volume/manager) should be done to make sure
we're being efficient here and not doing another get after
every update.

Change-Id: I0464d1879571a0044a416d652a186b1462c57fa2
Closes-Bug: #1349912
Merge "Add return of updated object on update from DB"