CBQE-2432: add additional subqueries test

Change-Id: I06ab31b2c58416da095f1bb0ea9a3999fe64ad9b
Reviewed-on: http://review.couchbase.org/42206
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: buildbot <build@couchbase.com>