CBQE-0: fix incremental_rebalance... stuck

due to unable to load data when rebalalance stuck

Change-Id: I380005728b13a9071d7fbd89daa9c5d7b59c3387
Reviewed-on: http://review.couchbase.org/36833
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>