CBQE-927: offline_cluster_upgrade with failover

test failed now due to MB-7490

Change-Id: Ib112fb43d1fb4d26aa11ba7679d3a742e9d905a8
Reviewed-on: http://review.couchbase.org/23700
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>