set metrics logger to be non additive

Problem: Turns out the metrics are going to the root logger and making it into stdout. After a bit of research learned java loggers are additive. Children of root loggers propagate messages to appenders higher up the hierarchy. This happens unless you set `additivity` to false in which case the metrics logger should not send log message to its ancestor loggers (in this case root logger). 

@udnay @airhorns