qemu: fix guestfwd chardev option back how it was
    
    Since commit d86c876a66e320b55220d00113027c9ad6199cff we are using
    guestfwd=tcp:IP:PORT,chardev=ID for guestfwd specification, however,
    that has not changed in qemu, so guestfwd does not work since.
    
    Apart from that, guestfwd is not working with older qemu that doesn't
    have QEMU_CAPS_DEVICE.
    
    Both regressions exist since late 2009 and nobody found that (until
    now), so I'm only fixing the first one.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1112066
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>