CBQE-1521: _wait_for_replication_to_catchup always successful

Change-Id: I1afa096e711e0fab650ff2c0a8281793ca353476
Reviewed-on: http://review.couchbase.org/28364
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>