CBQE-2337 - Implement logic to verify number of vbuckets distributoion after rebalanace and failover

Change-Id: I084a3f23a833ed98e1dc46ff585fec04c935bb2a
Reviewed-on: http://review.couchbase.org/39505
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>