MB-10773 Handle dropping of connection gracefully

Currently if the connection to the UPR producer drops we end in an
error. This should be handled more gracefully.With this change, it
do retry and creates a new connection to the UPR producer.

Change-Id: Ie63c1581f025484420f9a50a8c7a0ad1c5304660
Reviewed-on: http://review.couchbase.org/36701
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>