what's important:
* if task code ran, it exits with 0. this code is regardless of (error, result)
* when it exited cleanly, we will get the values from the database
* if task timed out, the box code kills it and it has a flag tracking timedOut. we can
ignore exit code in this case.
* if task code was stopped, box code will send SIGTERM which ideally it will handle and end with 70.
* if task code crashed and it caught the exception, it will return 50
* if task code crashed and node nuked us, it will exit with 1
* if task code was killed with some unhandleabe signal, taskworker.sh will return the signal (9=SIGKILL)
https://forum.cloudron.io/topic/13408/update-to-cloudron-8.3-error
We get a Task xx crashed with code null in the notification.
The crux of the issue is that we use KillMode=control-group. This ends
up sending SIGTERM signal to box code and all the sudo in parallel. The box
code then sees the sudo die and records the task as failed.
To fix, we switch to KillMode=mixed. This gives box code a chance to handle SIGTERM
first. It cleans out its task list and kills all the sudo.
BindsTo will kill all the tasks when systemctl stop box is executed.
But when restarted, it keeps the tasks running. Because of this behavior,
we kill the tasks on startup and stop of the box code.
