Ros_launch.sh and example

[fbrand-new]

Proof of concept for a workaround that allows the user to run ros2 launch files from yarpmanager and correctly stop the nodes managed by the launch file.

Currently ros2 launch is not stopped correctly by a SIGTERM signal (ros2/launch#666) which leaves the underline nodes dangling. Unfortunately for us this is exactly what happens under the hood when we stop from yarpmanager.

Of the many possible workaround to fix this behaviour I propose this one since it allows us to modify the applications that need it once for all and we don't have to worry about it at runtime nor we risk introducing regressions in yarprun.

I am also leaving an example attached. I am open to discuss if it would be worth to transform this in a piece of software more structured than this - admittedly rough - bash script

[ciandonovan]

Hi @fbrand-new, this pull request fixes the SIGTERM handling issue ros2/launch#712. We use it internally with systemd and Podman containers as they send SIGTERM and not SIGINT (what ROS Launch expects) by default as part of the shutdown process.