Adds support for Floating IP

Just to add a real example: take the [CloudApi#updateVirtualMachine](https://github.com/jclouds/jclouds-labs/blob/master/abiquo/src/main/java/org/jclouds/abiquo/features/CloudApi.java#L775-L789) method in the Abiquo API.

When modifying a virtual machine in Abiquo (by adding a NIC or disk for example), the API returns a *202-AcceptedRequest* and a reference to a task to keep track of the progress of the operation, or a *204-NoContent* if the operation completed synchronously without the need of generating a task. It returns a task if the operation takes time to complete, or just returns void/null if it completed immediately.

If we added the 404 fallback to this method, then the user wouldn't be able to differentiate the case when the update operation succeeded and completed immediately and the case when he operation failed because the resource did not exist.