CBQE-0: raising exception when rebalance hangs, currently it silently skips after printing error statements

Change-Id: Iba9cdeeb35f0fd067ab8e4f5b15f9f33690886fc
Reviewed-on: http://review.couchbase.org/41565
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>