Boxes break the build-system abstraction.

[charlielye]

Boxes seem to have built upon other peoples anti-pattern of having it's own "run_tests" script that needs a whole load of build-system context.

The build-system should provide all you need such that a developer adding a project just:

• Writes a Dockerfile for their project (and optionally a compose file).
• Updates the build-manifest.yml
• Update circleci/config.yml (one day obsolete as will codegen from build_manifest.yml)

In config.yml you run something like cond_run_container or cond_run_compose.
Everything should be taken care of to execute a container, or compose file, which should then run whatever is expected to be run.

This issue requests getting rid of any code that replicates the build-system scripts in favour of the above approach.
Reach out to me if we're in some edge case that makes this not possible!

[charlielye]

Resolving as part of: #3727