Following work on reorganising the requires, there was an inconsistent
approach to where service wrappers are required. (Fog::Compute...)
Since they should be standardised and shared across providers (although
they really aren't yet) they have been moved to `fog-core` gem.
Each provider has their own `lib/fog/{provider}/core` files that is
required by each of their services. These files should all require
`fog/core` which already required most or these.
So this removes the extra cases to concentrate them in core.
* Handle case where droplet is locked pending events, DO support says
they are planning to expose something in the api to show these events.
Until then this is the best we have.
* Whitespace cleanup
* Refactor test helpers
* Use the collection helper for the digitalocean servers collection
