* Replace all `rlog` occurrences with the shared logger
* Use the same log format in `InitLoggerStderrOnly` as well
* Convert one more `log.Fatal` to `logger.Log.Errorf` as well in the `cli`
* Replace `log.` occurrences with `logger.Log.` in `agent`
* Fix `cannot use err (type error)`
* Change the logging level to `DEBUG`
* Replace an `Errorf` with `Fatal`
* Add informative message
* Renamed aggregator -> apiServer.
* Format errors with container names.
* Renamed collector -> apiServer.
* Rephrased help messages.
* Moved api -> agent.
* Continue renameing api -> agent in Makefile and Dockerfiles.
