main: hook up with discovery

@philips We need to modify current discovery to create _config/size key when new the token.
tested on my local machine, works. 
We should add log messages for the three (?) possibilities:
- "etcd: no log found in data-dir, initializing from discovery"
- "etcd: no log found in data-dir, initializing from bootstrap-config"
- "etcd: found existing log data, recovering"