added xdcrCheckpointing and nodesExt to bucket caps

Change-Id: Ibdb1a898db4f11e2242433d7365d92fae83a3f53
Reviewed-on: http://review.couchbase.org/40273
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>