InetAddressAndPort to extend InetAddress

Logically InetAddressAndPort encapsulates the same information as a simple InetAddress. Importantly, InetAddressAndPort cannot easily be unpicked from its dependencies that prohibit it being shared between classloaders. So our in-jvm dtest API instead uses SocketAddress. To support a clean and efficient Streaming API we need to be able to treat InetAddressAndPort as such a cross-classloader type.