Support ephemeral port binding

[Qwaz]

If publish_all_ports option is used, a container will allocate unused ports automatically when it starts.

To handle this scenario,

1. port becomes optional in run command and ops::run.
2. HostConfig uses publish_all_ports when external port is not specified.
3. ops::run returns the port number and image hash. Additional list image command would be needed in ops::run function.
4. User will see both image hash and port number in CLI.