CBQE-1347: add rebalance test with empty bucket

Change-Id: Ib0443ae6221f3cbf207e195f85130961dabf8ee1
Reviewed-on: http://review.couchbase.org/27044
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.salooja@globallogic.com>