CCBC-391: Preserve mc_SERVER across topology changes

See the bug for more details on the issue
Change-Id: I41ccb97c9b41196a7cd7070b07db75d3073df038
Reviewed-on: http://review.couchbase.org/36277
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>