tests: pad: tests for accept-caps default handling
tests: pad: tests for accept-caps default handling

Check if all the default 4 accept-caps possibilities are working:
subset or intersect check and query-caps or template caps comparisons.

https://bugzilla.gnome.org/show_bug.cgi?id=753623

jpxiong/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,centricular/gstreamer,centricular/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,centricular/gstreamer,krichter722/gstreamer,jpxiong/gstreamer