Previously, k3s.service was failing when the EnvironmentFile does not exist:
```
Feb 02 17:17:30 suda-ws01 systemd[1]: k3s.service: Failed to load environment files: No such file or directory
Feb 02 17:17:30 suda-ws01 systemd[1]: k3s.service: Failed to run 'start' task: No such file or directory
Feb 02 17:17:30 suda-ws01 systemd[1]: k3s.service: Failed with result 'resources'.
Feb 02 17:17:30 suda-ws01 systemd[1]: Failed to start Lightweight Kubernetes.
```

ref: https://unix.stackexchange.com/questions/404199/documentation-of-equals-minus-in-systemd-unit-filesSigned-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>