CBQE-2383: tuq add union tests

Change-Id: Idcb30e7b2afcf3dca3b51930d31fd5234ec8ef03
Reviewed-on: http://review.couchbase.org/40752
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: buildbot <build@couchbase.com>