CBQE-2304 fix case that adds 1 more node to rebalance
so total node more than nodes_init and we could collect more nodes than initial nodes

Change-Id: I30586dc4dd4c8a2aa8684e998dfcc9e6729a00d8
Reviewed-on: http://review.couchbase.org/39332
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>