Logging - Implement dynamic log levels in ofagent

Implement the design created in VOL-900 in the OfAgent. This involves watching for changes in Etcd, evaluating log levels in the required priority (most specific loglevel has the highest priority, least specific loglevel has the lowest priority), and dynamically configuring the log level of the openolt adapter.

Same basic task as VOL-2310 but applied to OfAgent instead of adapters. There are two Ofagents (python and go). I suggest working on the go one and ignoring the python one.