sendHeartbeat(localNode) {
		return this.publish(
			new Packet(P.PACKET_HEARTBEAT, null, {
				cpu: localNode.cpu
			})
		).catch(
			/* istanbul ignore next */ err => {
				this.logger.error("Unable to send HEARTBEAT packet.", err);

				this.broker.broadcastLocal("$transit.error", {
					error: err,
					module: "transit",
					type: C.FAILED_SEND_HEARTBEAT_PACKET
				});
			}
		);
	}
Send a node heartbeat. It will be called with timer from local Discoverer.

@params {Node} localNode
@memberof Transit