WIP: Spawn-friendly ftp-server and http-server

Adjust SimpleFTPServer and SimpleHTTPServer to be spawn-friendly in that they don't pull in non-picklable things when they launch.

This fixes remaining spawn unit test breaks under tests/.

Note that the integration tests are still disabled, we'll tackle those separately.

We're also not enabling all the unit tests, just the ones under tests/, we'll tackle the others separately too.