[bug] Rosmaster URI export does not work

[ZygaOGC]

(Please add appropriate labels)

• Windows: (Version)
• Linux: (Ubuntu/20.04)
• ROS 1: Dist
• ROS 2: Dist

<0.8.0>

what is the bug

Can not launch debugging with a remote rosmaster.

Repro steps

1. Export ROS_MASTER_URI variable in the pre-launch task.
2. Launch debugging

expected behavior

Node under debugging should connect to the rosmaster available at exported URI

[ranchhandrobotics]

Unfortunately, VSCode itself does not propagate environment variables between tasks, so this is lost well before the ROS extension activates. Instead you should launch vscode from a pre-initialized environment, or ensure that you are using ros from a root install. Check out this video for more details: https://www.youtube.com/watch?v=N2vqBvPQdhE

[ooeygui]

I'm adding support for specifying a setup script by full path instead of just attempting to inferring. This resolves some issues where ROS isn't installed in a standard location.

[ooeygui]

Support for arbitrary script loading has been added in #678