createiso: Create Joliet tree with xorriso
    
    This structure is important for isoinfo -J, which is in turn called by
    virt-install.
    
    This can be tested by using a bootable ISO by modifying it with a dummy
    additional file and preserving boot records:
    
        $ xorriso -indev netinst.iso -outdev test.iso -boot_image any replay -map setup.py setup.py -end
        ...
        $ isoinfo -J -i test.iso
        isoinfo: Unable to find Joliet SVD
        $ rm test.iso
        $ xorriso -indev netinst.iso -outdev test.iso -joliet on -boot_image any replay -map setup.py setup.py -end
        ...
        $ isoinfo -J -i test.iso
        $
    
    Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2144105
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>