Test python nodes sometime exit with segfault

[christophfroehlich]

Describe the bug
Sometime the shutdown fails with a segfault:

[INFO] [publisher_forward_position_controller-9]: sending signal 'SIGINT' to process[publisher_forward_position_controller-9]
Error: ROR] [publisher_forward_position_controller-9]: process has died [pid 37985, exit code -11, cmd '/home/runner/work/ros2_control_ci/ros2_control_ci/.work/target_ws/install/ros2_controllers_test_nodes/lib/ros2_controllers_test_nodes/publisher_forward_position_controller --ros-args -r __node:=threedofbot_position_command_publisher --params-file /home/runner/work/ros2_control_ci/ros2_control_ci/.work/target_ws/install/ros2_control_demo_example_13/share/ros2_control_demo_example_13/config/three_robots_position_command_publishers.yaml'].

To Reproduce
ros-controls/ros2_control_ci#477

Additional context
How do we have to properly shutdown a python node?
#1400