Ensure that arguments to Mixlib::Log#add are passed as is to all loggers

I'm attempting to wrap mixlib log with ActiveRecord::TaggedLogger which calls #add on the logger it wraps, it so happens that Mixlib logger breaks in such a situation because it does not pass the arguments transparently to the loggers that it wraps in turn. Thereby causing the logs to print a log message with blank message in it.

For the implementation of TaggedLogger see https://github.com/rails/rails/blob/v3.2.6/activesupport/lib/active_support/tagged_logging.rb#L35