Mock classes belong to test

[gildub]

The various Service's Mock classes belong to the tests section, namely test/.

For more details, please see conversation in fog-core [1]. Although the work happening in fog-core should be completely transparent for fog-openstack, we might follow same approach (or not) of using an external gem (fog-mock-openstack) for keeping all Mock code.

This could happen in stages, initially separating the Mock classes and related code from the source code.

[1] https://github.com/fog/fog-core/issues/198