CBQE-2187 Add Verification Library for Rebalance and Failover Tests

Change-Id: Id44cd1d66731542f6572f0d1925fbf1df346c71f
Reviewed-on: http://review.couchbase.org/35413
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>