restart=on-abort when running as init-process

[gdraheim]

While systemctl.py will be dead in most circumstances, it is in fact a continuous process when it is the PID 1 in a docker container. At that place it may be useful to not only check for zombies regularly but also for dead process that a restart=on-abort rule in their service config. With the help of a pid file one can check for the condition regularly and run "start" again if it was found dead. That can help so people do not try to write watchdog wrappers for the services file which the systemd world has already mitigated.