CBQE-0: fix incremental_rebalance_out_with_queries stuck

http://qa.hq.northscale.net/job/centos_x64--02_04--Rebalance_tests_UPR-P0/24/consoleFull

Change-Id: I2b03f0ad8428c98021722daee1cee87e77fbde2a
Reviewed-on: http://review.couchbase.org/36391
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>