CBQE-0: minor changes in incremental_rebalance_in_out_with_mutation_and_expiration

Change-Id: I0603abbfd0adfd2c1ac80aa383bf73ce4f63fd5c
Reviewed-on: http://review.couchbase.org/27246
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>