CBQE-0: fix incremental_rebalance_out_with_mutation_and_deletion stuck

http://qa.hq.northscale.net/view/3.0.0/job/centos_x64--02_04--Rebalance_tests_UPR-P0/108/consoleText

Change-Id: Id42a101ad947c9ed137aec3f780f0041a27686bf
Reviewed-on: http://review.couchbase.org/37276
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>