All other services should be added to SYSTEMD_SERVICES_* and
handled by rootfs image script.

Use chrony as NTP client.

Due to race with livecd-timezone.

Thanks boyarsh@ for m-p-d implementation and sem@ for the hint.

- xfce-utils removed from Sisyphus
- apt-indicator needs gksu
- add slinux misc packages:
  + pm-utils
  + strace
- image-scripts.d/50services is a script which starts/stop some services