Launch files should exit with higher priority nodes exit

[hello-binit]

If I launch navigation.launch.py (which includes stretch_driver.launch.py internally), and the stretch_driver node exits, then the nav launch file should exit out with error too. Similarly, if the RPLidar dies, so should nav.

This applies whenever a launch file includes a driver, but it can also apply if your application depends on a planner. For example, my application requires /head_scan from FUNMAP. If the FUNMAP process dies, I want my launch file to error out, instead of reporting the error is a sea of unrelated warning/errors.

Typically, when a node dies, it does along a TF with it. When a transform goes missing, a lot of nodes start spewing warnings/errors to the console. This makes it easy to miss the root reason why the system failed. If everything exited when the original node died, it would be easier to find the traceback from the original node.