[Audit] Rewrite go-cbaudit to allow unit testing and move it into tools-common

What's the issue?
We want to improve upon go-cbaudit to add the ability to handle retrying requests where possible. This is going to be more difficult with go-cbaudit as it stands as it's not currently unit tested.

What's the fix?
We should look at incorporating go-cbaudit into tools-common whilst adding testing (as is required in tools-common).