Configure pupernetes with a config file

[JulienBalestra]

Allows users to override the defaults by a yaml config file.

Features I have in mind:

• everything configurable today by flags
• manifests (Kubernetes, systemd units) see
  • configure the kubelet cAdvisor port
  • configure the kubelet read-only port
  • configure the kubelet AuthN/Z (today it's secured by default), we might want to setup a self-signed endpoint

[JulienBalestra]

This issue is tied with #40