Make JRuby before command hook work on Aruba environment

[mvz]

Summary

Make the JRuby before command helper modify the Aruba environment, rather than the real one.

Details

The JRuby helper sets up a before :command hook to set helpful environment variables for JRuby. This changes makes the helper use set_environment_variable to set Aruba's environment rather than directly modifying the real one.

Motivation and Context

When the environment is modified directly, this causes unexpected behavior when using with_environment, since that methods will base the changed environment on the environment at startup, rather than the current one. Therefore, with_environment will unexpectedly undo such modifiections.

All this came to light while working on #603.

How Has This Been Tested?

Tests for the JRuby helper were updated to check the result inside a with_environment block, thus mimicing the behavior when the hook is used before running a command.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I've added tests for my code

[olleolleolle]

The tests now read exceptionally well, and the implementation code is clearer as well.

And the tests pass!