[WIP] Docker cleanup

Currently working at breaking the Docker stuff out a bit more.

- [x] Rename `rando.py` to `orchestrate.py`. I'm open to naming suggestions.
- [x] Fix a current intermittent bug when a container doesn't exist for some reason

I'd like to see the actual spawner be separate from the outer endpoint, so the tornado application that handles the `/spawn` route doesn't actually have pure access to the Docker socket (or root).