CBQE-2343: n1ql subqueries tests

Change-Id: Icbbeaf69b3c003d51816af627946bea6803d5acc
Reviewed-on: http://review.couchbase.org/41254
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: buildbot <build@couchbase.com>