Tweak desktop_vt tty detector a bit
    
    The intent is that if the ps check finds nothing we'll use the
    loginctl output, but that doesn't work because script_output
    doesn't return the output if the script fails. There's an arg
    you can pass to make it do so, but let's just make it always
    succeed instead, by adding a ||: to the second grep like we have
    for the first.
    
    Also, I noticed this problem because the ps check started not
    working on F36 KDE because none of the processes we check for
    are shown as running on a tty, so let's add one more that *is*
    shown as running on a tty...
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>