CBQE-0: try to fix measure_time_index_during_rebalance stuck

http://qa.hq.northscale.net/view/3.0.0/job/ubuntu_x64--30_00--Rebalance_UPR-P0/36/

Change-Id: I5e747d2b75aada3c5fb7a419dee076e13070fb7e
Reviewed-on: http://review.couchbase.org/37072
Reviewed-by: Parag Agarwal <agarwal.parag@gmail.com>
Tested-by: Parag Agarwal <agarwal.parag@gmail.com>