Unify host port api
This MR unifies the host port API as proposed by #21 (closed). The protocol associated with each port mapping is ignored and not exposed the user. I see no immediate use case for the protocol part and it makes the API a bit cleaner by leaving it out. If a use case turns up later we could add it then.
Note: The implementation will perform teardown and return an error to the user if we fail to extract the host port mappings.