CBQE-2449: add tests for EXCEPT

Change-Id: Ibe89e1ba80e5537db8bb4456fc5e7d4ce4b96b79
Reviewed-on: http://review.couchbase.org/43685
Reviewed-by: Ketaki Gangal <ketakigangal@gmail.com>
Tested-by: buildbot <build@couchbase.com>