manager: add systemd.show_status=auto mode

manager: add systemd.show_status=auto mode

When set to auto, status will shown when the first ephemeral message
is shown (a job has been running for five seconds). Then until the
boot or shutdown ends, status messages will be shown.

No indication about the switch is done: I think it should be clear
for the user that first the cylon eye and the ephemeral messages appear,
and afterwards messages are displayed.

The initial arming of the event source was still wrong, but now should
really be fixed.