Comment 2 for bug 1841036

When building with a version of charm-tools with the unreleased https://github.com/juju/charm-tools/commit/1ffd2b3130690f588c03ee748d106d020e76db54 commit in it this would not have been a problem, as it cleans up after itself.

However, this would probably raise build concurrency issues like we see in bug 1733984.

I feel we need some more sandboxing around the build process with clean per instance caches for pip, charm-tools etc.