CBQE-927: offline_cluster_upgrade_and_rebalance

Change-Id: I502a4507d2c9b910330d6ef4ca92a2069cb9648d
Reviewed-on: http://review.couchbase.org/23677
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>