Move all fog classes to `core/fog`

Also change the includes files to include the new locations.

Committing a breaking change to keep the commit history easy to parse.
Move fog unit tests to core directory
Namespace all fog classes into Core
Use new `Core::Fog::ServiceInterface`
Use new `Core::Fog::ModelInterface`
Use new `Core::Fog::Login` class
Use new `Core::Fog::ContentTypes` class
Use new top level fog class
Add temporary `fog.rb` and `ModelInterface`

These are required because vCloud Core has a dependency on vCloud Tools Tester, which requires both these files. Once vCloud Tools Tester is updated to use the vCloud Core with these changes, these files can be removed.
Move two more fog tests to correct location

There is one remaining fog test to move, but moving it causes an error due to the ordering, so I'm going to move and fix that in a separate commit.
Add FIXME to test that clears ENV

I have punted this to a bug in Pivotal https://www.pivotaltracker.com/story/show/76118720.
Revert "Add FIXME to test that clears ENV"

This reverts commit 8a4e27392805de7ab1e8ef4f14b0e76b171ad328.

Has been fixed by e766457 and 09ef65f on master.
Merge branch 'master' into fog-to-core

Conflicts:
	spec/integration/fog/login_spec.rb

Conflict is caused by a change of class name in the outer describe block.
Relocate spec/integration/fog/login_spec.rb

This was omitted in eaebabd. The problem has since been fixed by #110.
Merge pull request #108 from gds-operations/fog-to-core

[#70162466] Move fog to core directory