MB-11924: added ns_ports_setup:sync

So that we can wait until current round of ports synchronizations is
complete.

Change-Id: Id9a41e32d8ab7edb1678e084a4b4869718c55880
Reviewed-on: http://review.couchbase.org/42014
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>