CBQE-1206 fix bug for not able to failover and add_back

Change-Id: Ic8793bc2ebd3cd3bebe4e82999c1b9a64c34fe92
Reviewed-on: http://review.couchbase.org/25744
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>