CBQE-0: rebalance_reached doesn't work when rebalance hangs

when rebalance hanges on 'rebalance percentage : 0 %' rebalance_reached return true

Change-Id: I8511929a52dbea78ca88dce231638cc1b82dbaf0
Reviewed-on: http://review.couchbase.org/33257
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>