Support for creating a container with floating IP address

[hongbin]

We would like to add support for creating container with floating IP address (with one command). For example, we can expand the option '--net' to add a 'public-network' option as below:

  $ zun run --net network=<private_network_id>,public-network=<public_network_id>

Then, this command will create the container, create a neutron port from <private_network_id>, create a floating IP from <public_network_id>, and assign the floating IP address to the neutron port.