Re-order shutdown vs node destruction (#213)

I'm not sure if calling Node.destroy_node() while another thread is
spinning was ever supported, but it definitely causes problems.

Signed-off-by: Scott K Logan <[email protected]>

Author: cottsay

test_launch_ros/test/test_launch_ros/actions/test_load_composable_nodes.py

@@ -76,8 +76,8 @@ def load_node_callback(self, request, response):
 
     def shutdown(self):
         self._executor.shutdown()
-        self.destroy_node()
         rclpy.shutdown(context=self._context)
+        self.destroy_node()
         self._thread.join()