util module for repo setup/teardown

[hackergrrl]

Via @diasdavid:

It would be pretty sweet to grab this func and also the logic to 'inject' a go-ipfs repo (found in index.js and browser.js) and make a utils file that can be used across tests that can 'create and teardown a go-ipfs generated repo' and 'create and teardown a fresh baked repo.

[daviddias]

TODO:

• util module https://github.com/ipfs/js-ipfs/blob/master/test/utils/temp-repo.js