Automatically add existence tests #108

I am not sure if it is a good idea or on some platforms it slow down the build process too match (especially on windows), but it would be interesting to automatically add an existence tests for ros pkg, to early catch runtime install conflicts such as RoboStack/ros-jazzy#125 .

At the moment, we manually add this test for some key packages:

tests:
  # Regression test for https://github.com/RoboStack/ros-jazzy/issues/125
  - script:
    - ros2 pkg prefix desktop

but ros2 pkg prefix <rospkgnamewithoutprefix> should be true for all ROS pkgs.