Sync kombu_reconnect_delay from Oslo

When reconnecting to a RabbitMQ cluster
with mirrored queues in use, the attempt to release the
connection can hang "indefinitely" somewhere deep down
in Kombu.  Blocking the thread for a bit prior to
release seems to kludge around the problem where it is
otherwise reproduceable.
The value 5.0 fits for low perfomance environments as well.

Cherry-picked from Oslo.messaging:
fcd51a67d18a9e947ae5f57eafa43ac756d1a5a8
Related-bug: #856764

Change-Id: Ifadda4dd9122df9ccb4ecf560ce3db3e38adf2b9
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
Merge "Sync kombu_reconnect_delay from Oslo" into stable/icehouse