This functions are working as follows:
- Send a SIGTERM to all processes that may be finished
- Send a SIGKILL to all processes that still live and may be finished
- Try to unmount all mount points
- Try to remount read-only all mount points that can't be umounted
- Umount all swap devices
- Umount and detach all loopback devices
- Call [poweroff|halt|reboot|kexec]
TODO:
- Umount device-mapper.
- Make log work. So far it is being useless as we do not parse
/etc/systemd/system.conf, kernel command line but just
environment, however we're executed by init and thus have no
useful variables. Forcing it to target=kmsg/console and
level=debug also does not produce any output, however writing to
/dev/console does work (hack used during debug).
