CBQE-1706 incremental_rebalance_in_out_with_mutation_and_expiration hangs

Change-Id: Ibbfac842a5f3278be474989b738d1fce0bd79bce
Reviewed-on: http://review.couchbase.org/30377
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>