[podman] conmon should restart dead child processes

## What's the issue?
When killing `slirp4netns`, a pod or a container keeps on running without warnings, but without networking.

## How to reproduce?
``` sh
podman pod create --name systemd-pod
podman create --pod systemd-pod alpine top
podman create --pod systemd-pod alpine top
podman pod start systemd-pod
pkill -U tobwen 'slirp4netns'
```

## What's expected?
1. _conmon_ (or _podman_) should take care of the child processes and restart them if they crash or die.
2. A notification in the logs would also be nice.

## What's the environment?
podman `version 3.3.0-dev`
conmon `version 2.0.30-dev`