iframe playlists will be given a name based on the output name of
the main stream. This is done to ensure unique filenames between
different video output streams.
Change-Id: Id0de9c5834599e9d896243e30569c55f34e7cd68
Instead of using the test file's index in a list to create the output
name, use the original filename and the descriptor.
This caused some problems with file name collisions when some tests
were using the same name. That was fixed by changing the names. This
will go away once they are transitioned to use DiffDir like the other
tests.
Change-Id: I0a4c480406705ca63fcea61c86c67d4a5f739295