Bug#758917: reboot should not return shell prompt

[積丹尼 Dan Jacobson]

Package: systemd
Version: 208-8
File: /lib/systemd/system/rescue.service

I notice when typing "reboot" from the rescue (etc.?) shell that one
gets the shell prompt back right away, and thinks 'well that didn't
work,' and goes on typing commands... and then after a few seconds,
mid-command, finds it really did work.

Therefore it would be best to just print some dots and sleep, else the
user might do things when it is best 'to just stop playing on the train
tracks as here it comes.'