Adds support for Floating IP

>In virtually all cases I have seen (update operations) it means a missing resource (nothing to update - always 404 related).

Agree, but that's just because you know well the API. I know several APIs that return 204 on update operations, with a location header with the URL of a task to keep track of the progress of the operation, and a 204 would translate to a null body/returned object. No difference on the client side than a 404 response, but with a significant difference on the success/failure of the operation.

I mean, you can make assumptions because you know well the API. When you use a provider you're not that familiar with, a `null` value might not give you enough information to know what happened and what you need to fix. Or even enough information to know if there is an issue on your side! Imagine an update operation in the ElasticHosts API that returns null. Are you sure you would properly understand it?

That's how users using the OpenStack providers and APIs may feel when seeing this kind of methods returning `null`, so I'm a big +1 on stop using this pattern and opening an issue to change it wherever it is applied.