anaconda: end install immediately if we see the error screen
    
    If install errors out, currently we still wait like an hour for
    an "install_done" screen that will never come, before we give
    up. Since we have a needle for the "unknown error has occurred"
    screen, we may as well use it here - if we see that screen, we
    can just die immediately. This may go stale if we forget to
    update the needle, but it's only one line, so meh.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>