CBQE-949: fix rebalance_in_out_at_once_persistence_stopped

we don't know exactly how many active and replica items need to drain after rebalance with stopped persistence

Change-Id: I3f1312a26c1cffa01d17d9d3e29da2db035cb993
Reviewed-on: http://review.couchbase.org/23683
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>