[mtvservices:embedded] Use another endpoint to get feed URL

Closes #10363

In the original mtvservices:embedded test case, config.xml is still used
to get the feed URL. Some other examples, including test_Generic_40
(http://www.vulture.com/2016/06/new-key-peele-sketches-released.html),
and the video mentioned in #10363, use another endpoint to get the feed
URL. The 'index.html' approach works for the original test case, too. So
I didn't keep the old approach.