Implement graceful handling of agent restart

[soenkeliebau]

Once we have implemented systemd for running services in #5 , we need to look at identifying agent restarts and gracefully handling that.

Basically the test upon startup needs to be

• check if config directory for current pod version exists
• if yes, assume service should be running and check state
• if not: start service with current config
• Remove current Krustlet behavior to evict (=delete) pods upon shutdown