MB-10179: [xdcr] publish more per-vbucket details with vb stats

Change-Id: Ib10d6e8fd9387ea757252f9f390a89f0e8f86e74
Reviewed-on: http://review.couchbase.org/40361
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>