change prefix for xdcr related upr connections to xdcr:

Change-Id: Iec3b6096757e8298ab23773583ec8d316ac4504c
Reviewed-on: http://review.couchbase.org/37404
Reviewed-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Artem Stemkovski <artem@couchbase.com>