Add logging to zentity

[davemoore-]

zentity should take advantage of the logging architecture of Elasticsearch to aid troubleshooting. This can be implemented as needed instead of creating a dedicated feature branch for logging.

To implement this:

1. Add the following property to any class that will use the logger (substituting CLASS_NAME with the name of the class):

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

class MyClass {
   private static final Logger logger = LogManager.getLogger(MyClass.class);
}

2. Invoke the logger's methods as needed:

logger.catching(e);
logger.fatal(message);
logger.error(message);
logger.warn(message);
logger.info(message);
logger.debug(message);
logger.trace(message);

3. Add the following configurations to the elasticsearch.yml file of each node to write the log messages to the Elasticsearch log files:

logger.org.elasticsearch.plugin.zentity: DEBUG
logger.io.zentity: DEBUG