Stop logging deadlock tracebacks

Stop logging deadlock tracebacks

The oslo db retry decorator logs a traceback everytime a deadlock
is encountered even though it is being retried. With multiple workers
and a Galera cluster, deadlocks are common occurences due to our use
of with_lockmode update so we should not be polluting the logs.

This patch adjusts our usage of the retry decorator to catch deadlocks
with the exception checker which does not log them until the retries
are exhausted.

Change-Id: I433fbbad61070e20ebe934b9247e36fc190fa3e0