CBQE-2177:: Adding support for delta rebalance+some basic tests

Change-Id: I240ba165277dcfebe28299a03135ed5165d078b3
Reviewed-on: http://review.couchbase.org/35424
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>