CBQE-2284:: Add UPR Flow control logic checking in rebalance tests

Change-Id: I44def2e03d78e0a7418386fce11a11196a303b7c
Reviewed-on: http://review.couchbase.org/37827
Reviewed-by: Ashvinder Singh <ashvinder@couchbase.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>