tools: move message listener to worker objects

Moving the `message` event listener from the cluster object to each
worker object allows easier backporting of the recent jslint
changes since v5.x and older do not have v6.x's `worker` parameter
in the cluster object's `message` event.

PR-URL: https://github.com/nodejs/node/pull/6212


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>