[rel-2.2.0] switch ns_server to branch 2.2.0

Change-Id: I9a850a0b8dd5f9abebc6d1679e2d5d95b0bc230a
Reviewed-on: http://review.couchbase.org/27509
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>