MB-11551 support for querying upr-vbtakeover stats

Change-Id: I8f95fb4cd3612db6acce20c82d2f4d4f4a4e970c
Reviewed-on: http://review.couchbase.org/38977
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>