[libvirt-tck] scripts: fix disk media change test

[Erik Skultety]

On Mon, Mar 23, 2020 at 05:09:24PM -0600, Jim Fehlig wrote:
> Since the introduction of the 'index' attribute of a disk's
> <source> element, test 207-disk-media-change.t is failing. The
> test is a bit flawed in that it compares initial and final domXML
> after changing the media of a cdrom disk device. The test only
> needs to check the final domXML to ensure the correct <source>
> path exists at the end of the test.
>
> Signed-off-by: Jim Fehlig <jfehlig at suse.com>
Reviewed-by: Erik Skultety <eskultet at redhat.com>