Fix SimpleCov integration

[mvz]

Summary

Activates simplecov on nested processes. It works, but makes the tests very slow. Based on #898 but with a more minimal change.

This should probably be hidden behind an environment variable.

Details

• Fix simplecov setup for cucumber features
• Switch formatters for child process to avoid unwanted output
• Remove unused SimpleCov Formatter monkey-patch

Motivation and Context

PR #898 is stale.

How Has This Been Tested?

I ran cukes. It looks like it tries to calculate coverage for files in tmp/, and maybe even loads simplecov inside the aruba-test-cli and other test executables.

Types of changes

• [x] Internal change (refactoring, test improvements, developer experience or update of dependencies)

Checklist:

• [ ] I've added tests for my code
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.