Remove majority of logic from `build/__init__.py` for cleaner imports fixes #194

[marcoceppi]

Remove majority of logic from build/__init__.py for cleaner imports fixes #194

Checklist

• Have you followed Juju Solutions hacking guide?
• Are all your commits logically grouped and squashed appropriately?
• Does this patch have code coverage?
• Does your code pass make test?

[marcoceppi]

Still testing if this addresses autopkgtests