Skip post-install actions for VNC client installs
    
    ...otherwise the VNC client tests fail on aarch64 because we try
    to apply the 'console=tty0' workaround for #1661288. Fortunately
    we don't really need that for the VNC install test to work, so
    let's just skip it. We can make this more sophisticated later if
    it turns out to be necessary.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>