move spin functions to nodehandle

src/examples/publisher/publisher.cpp

@@ -90,7 +90,7 @@ PX4_MAIN_FUNCTION(publisher)
 		 */
 		rc_channels_pub->publish(msg);
 
-		px4::spin_once();
+		n.spinOnce();
 
 		loop_rate.sleep();
 		++count;

src/examples/subscriber/subscriber.cpp

@@ -85,7 +85,7 @@ PX4_MAIN_FUNCTION(subscriber)
 	 * callbacks will be called from within this thread (the main one).  px4::spin()
 	 * will exit when Ctrl-C is pressed, or the node is shutdown by the master.
 	 */
-	px4::spin();
+	n.spin();
 
 	return 0;
 }