MB-12564: send crud attempt requests only to bucket nodes

Change-Id: Ie51cf9a80dfed935159c21832e37dc5b02ed2d76
Reviewed-on: http://review.couchbase.org/42937
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>