List port mappings for the CONTAINER, or lookup the public-facing port that is NAT-ed to the PRIVATE_PORT

# EXAMPLES

    # docker ps
    CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                                            NAMES
    b650456536c7        busybox:latest      top                 54 minutes ago      Up 54 minutes       0.0.0.0:1234->9876/tcp, 0.0.0.0:4321->7890/tcp   test

## Find out all the ports mapped

    # docker container port test
    7890/tcp -> 0.0.0.0:4321
    9876/tcp -> 0.0.0.0:1234

## Find out a specific mapping

    # docker container port test 7890/tcp
    0.0.0.0:4321

    # docker container port test 7890
    0.0.0.0:4321

## An example showing error for non-existent mapping

    # docker container port test 7890/udp
    2014/06/24 11:53:36 Error: No public port '7890/udp' published for test