System log and its collector

[takaoka-youta-opst]

Now, Knitfab's system component (knitd, knitd_backend, event loops, ...) are logging sepalately.

• To read logs, we needs kubectl logs for each containers.
• No (comprehensive) performance and error logs in uniformed format.
• Data agent's logs cannot be read.

So, reading logs are hard thing.

• Add logs collector.
• Define log format.