Use ExposedPorts for --net=host

[wrouesnel]

Simple change to support the fact that docker no longer fills out mapped ports when run in --net=host mode. This instead simply reads all exposed ports and fills out the relevant service structure, restoring the original functionality.

Fixes #159

[ghostbar]

This is a very simple patch, I tested it and it's working. Please merge.

[mgood]

Thanks for looking into this, but what about containers that are not run with --net=host? From what I'm seeing in the API, ExposedPorts may work for --net=host now, though in other cases wouldn't you still need to use PortBindings in order to register the ports that are bound to the Docker bridge?

[wrouesnel]

ExposedPorts is always populated with the port number exposed on the host of any port (at least on Docker 1.9 on my laptop here).

If I run docker run -p 220:22000 -it debian /bin/bash, then I get

        "ExposedPorts": {
            "22000/tcp": {}
        },

back from docker inspect.

[albamc]

this patch is useful when you use macvlan modes too.

[josegonzalez]

This looks good to me. @MattAitchison can you give this a quick glance and tell me I'm not being dumb? It's mergeable otherwise :)