freeze ns_server in 3.0 builds

Change-Id: I481a0fe3d0a589d4ae8e8513c7d674ca0a32bb48
Reviewed-on: http://review.couchbase.org/32760
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>