Start head processes on the node.

def start_head_processes(self):
        """Start head processes on the node."""
        logger.info(
            "Process STDOUT and STDERR is being redirected to {}.".format(
                self._logs_dir))
        assert self._redis_address is None
        # If this is the head node, start the relevant head node processes.
        self.start_redis()
        self.start_monitor()
        self.start_raylet_monitor()
        # The dashboard is Python3.x only.
        if PY3 and self._ray_params.include_webui:
            self.start_dashboard()