testing/k3s: make k3s daemon run again

I installed the k3s package from testing. While trying to run it I got several error messages. The changes in this MR fix all found issues, but there might be more MRs to come.

There are still some warnings/errors, but these seem to be releated to kubernetes itself. The service starts up and its output is logged.

I used the original installer from https://raw.githubusercontent.com/rancher/k3s/master/install.sh as reference at some points in the init file.

Currently k3s does not support a way to signal "log rotation", so I restart it instead.