prevent hanging when renaming file

[sdondley]

For #1299

[ferki]

I'm afraid a full fix would be more involved than forcing the operation unconditionally on a single FS interface. See my comment on the issue.

Let's discuss the desired behavior of Rex and implementation details first over there.

[ferki]

As discussed on IRC, the minimum approach for this would be to:

• test for file writability in all the Rex::Interface:Fs::* modules before having a chance to hang on an interactive prompt, and raise an exception: the built-in is_writable function might help here
• fix all potentially affected methods: at least unlink would probably be affected as well, and there might be more, like rmdir

Also let's find a way to test at least a subset of those cases. Perhaps Test::Timer might help to detect hangs? Not sure how to kill the hung call though yet.

See more details on this comment.

If you'd like to keep working on this here, please mark the PR as draft, and feel free to update it as often as you need. Ideally, the first commit would be including tests that would fail, and then the follow-up commit(s) would fix that.