[BUG] Failed jail shutdown (due to timeout) leads to zombie pot

**Describe the bug**
We had a hanging promtail. On pot stop, shutdown timed out:

```
90 second watchdog timeout expired. Shutdown terminated.
Sat Mar  2 20:21:31 UTC 2024
jail: loki: sh /etc/rc.shutdown jail: exited on signal 9
```

But the jail was still there, with a half-broken devfs. Running pot stop a second time resolves the situation.

