Code review comment for lp://qastaging/~lamont/maas/bug-1651452

I'm not clear on what this branch fixes and why it's fixing it the way it does. I fear future readers won't have a clue why we have a horrible mess of regex matching and substitution here, and will be tempted to remove it, at their peril. ;-)

Could you please add some comments explaining the "why" for this change, and with a link to the bug? I had hoped that the bug report would contain some triage information, but it's rather empty, so it's hard for a naive person to figure out the reasoning behind this branch.

Also, please add a docstring to the new Python function you added. =)