wptagent log local logs syslog rfc5424

[FedericoMulas]

ref 177487

• Added log handler for syslog rfc5424 to support structured logging, ported from https://github.com/jobec/rfc5424-logging-handler/tree/master with BSD license because seems frozen and had needed issues pending (only 2 files where needed).
• Added new file rfc5424logging_context.py and relative class LoggingContext to store structured logging context to enhance each log while keeping backward compatibility with other types of logs.
• Added additional option --loglevel and refactored log level option handling into setup_logging class to support current log format an the new introduced rfc5424 log format.

After this PR is approved all log entries will be updated to add the new logging context.