[#70162466] Move fog to core directory

This is phase one of Operation Move Fog to Core.

There are a few things outstanding.

1. `fog.rb` and `temporary_fog_classes.rb` are required because vCloud Core has a dependency on vCloud Tools Tester, so until that has been upgraded to use the correct files, we can't get anywhere.

2.  There is still a test in `spec/integration/fog` – see https://www.pivotaltracker.com/story/show/76118720.

Anything else fog-related outside of the Core directory is an error; please let me know.

Phase Two involves hiding fog a bit more and should follow later today.