CBQE-1531: add explain tests for tuq

Change-Id: Ia1e6e67a123b65c9c819651b1b87b408f1e598af
Reviewed-on: http://review.couchbase.org/29470
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>