Adds support for Floating IP

There has been some recent discussion about this as per [JCLOUDS-678](https://issues.apache.org/jira/browse/JCLOUDS-678). Is it OK to silently return null if the resource the user is trying to update does not exist? I think that is correct for GET operations and DELETE ones (where the *expected state* is good if the resource already does not exist), but I think we should fail in other *write* operations.

Removing this fallback should propagate a `ResourceNotFoundException` which seems more appropriate in this case?