tests: Remove stale symlinks before linking loop device
    
    On storage setup we can have stale symlinks to loop devices
    which were created before reboot and now are gone. Re-running the
    setup will fail on creating the symlink again. In this patch we
    add removal of the stale symlink, if there is such, before symlinking
    the new loop device.
    
    Signed-off-by: Amit Bawer <abawer@redhat.com>