Reworking client tests, added more utils for fs testing, failing multipl...

This PR is about adding a bunch of tests for various ways that a client might interact with the server, and making sure the filesystem ends up in a state we expect.

This isn't ready to land yet.
It will only stop the current test, which is what you want. Mocha will keep going.

Honestly, this code is going away soon, so let's not worry.