tracker: Rely on the preinstalled multimedia demopack

The current test downloads from a legacy location the same contents already shipped by the official multimedia demopack under /home/shared.

On the target and SDK images it is wasteful and silly, as those exact contents come pre-installed.

On the minimal images this fails since there's not enough storage.

On the base SDK image the decision to not install the multimedia demopack was taken explicitly as it is not relevant there.

Change the test to only run on the images where it is appropriate and rely on the multimedia demopack being available out-of-the-box in /home/shared.