CBQE-1531: add concurrent queries with rebalance failover

Change-Id: I1abc99d2861c4c5020df39ee901018e6a0679e14
Reviewed-on: http://review.couchbase.org/29544
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>