Use a shell script to set environment variables for a kit

[timnoack]

This change addresses item #809

This adds a feature

The following changes are proposed:

• Added the possibility to use a shell / batch script that sets the environment variables for a kit.
• Added a unit test for this feature

Other Notes/Information

Some frameworks like the esp-idf / ESP8266_RTOS_SDK (ESP32 / ESP8266) use shell scripts to set the environment variables (especially update the PATH) for a build.

Uses the same approach as the function that gets the environment variables correspnding to a VS dev batch file (kit.ts collectDevBatVars)

[msftclas]

All CLA requirements met.

[not7cd]

@pisker, how easily do you think, one could source files?
I also found more related issues:
microsoft/vscode-remote-release#141
#288

[timnoack]

@not7cd the feature works by setting the filename of a shell script which is run during initialization. No source / call command is required.

One constrained is that the shell script is (currently?) not run in bash. The source command is bash specific so it is not available within the shell script. The "." command can be used instead.

[pkohout]

Any plans on when this will be released? Would really improve the vs code experience for us.

[timnoack]

@pisker, how easily do you think, one could source files?

The setup script is now run from /bin/bash. Because of that bash commands like source are available now