This will pass the first two arguments of roslaunch to roslaunch-complete. This is all we need. If it is only the launch file, only that will be passed. If it is pkg + launch, both will be passed. Any additional parameters like `roslaunch x.launch ARG` won't hurt.

The idea is that at this point we can't easily figure out what is intended. Someone might name the launch file `robot_bringup` (no .launch) or similar. This logic is left to roslaunch-complete to figure out in the same way that roslaunch does that. `rlutil.resolve_launch_arguments(sys.argv[1:])` is used in there to deal with the two possibilities of calling roslaunch. This makes sure we always behave like roslaunch would.