Improve handling of old ~/.localhost directory.

[ioquatix]

• Ensure tests are idempotent.

Types of Changes

• Bug fix.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.

[ioquatix]

@texpert @nogweii I have made a few improvements to the test, and extracted the path handling into the .path method. Would welcome your feedback as I think you mentioned some issues with this approach, but I'm leaning more towards it as it seems more predictable.

I found a couple of issues - I don't think the mv was working correctly. I've changed that to use Dir.glob.

Also, for the sake of testing, I've made it so it always runs in an isolated directory/root.

Localhost::Authority.path now accepts an env argument (and old_root: option). This allows us to test the path computation and old_root handling functionality independently of all the other code, which I think is now completely tested (we check the files are copied, etc).