advance ns_server's commit in 2.1-stable

Change-Id: I60d22282e6232625aa114d20923e0f6c2304e759
Reviewed-on: http://review.couchbase.org/23998
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>