JCLOUDS-198: Implemented the PagedIterable in Abiquo

Implemented the PagedIterable in Abiquo:

* Refactored all the domain objects to return Iterables instead of Lists, to allow a more flexible approach when using the PagedIterable.
* Added a generic PaginatedCollection that knows how to advance any paginated collection.
* Changed all methods from the Abiquo APIs that allow pagination to return the corresponding PagedIterables and PaginatedCollections.
* Added Expect tests for every paginated resource.