test-bot: uninstall all formula on cleanup.

[MikeMcQuaid]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew tests with your changes locally?

---

Need to do this manually now that we can't rely on git clean -xdf to do it for us.

[zmwangx]

I haven't looked at the code, but just want to make sure: this is for --cleanup only, right?

[MikeMcQuaid]

Yep.