[rel-2.5.0] point ns_server back to for-rackaware

Change-Id: I648969ca4b78467655381ce22c17902cadfd4f85
Reviewed-on: http://review.couchbase.org/31222
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>