CBQE-2231: tuq generator add handling unnest expressions

Change-Id: I5c46d7a944677b9b4b9365c84825e8c471e12a6a
Reviewed-on: http://review.couchbase.org/36705
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>