def docker_port(internal_port, container_name = name)
      docker_runner = Fleetctl::Runner::SSH.new('docker', 'port', container_name, internal_port)
      docker_runner.run(host: ip)
      output = docker_runner.output
      if output
        output.rstrip!
        output.split(':').last
      end
    end
def docker_port(internal_port, container_name = name)
      docker_runner = Fleetctl::Runner::SSH.new('docker', 'port', container_name, internal_port)
      docker_runner.run(host: ip)
      output = docker_runner.output
      if output
        output.rstrip!
        output.split(':').last
      end
    end
gets the external port corresponding to the internal port specified
 assumes that this unit corresponds to a docker container
 TODO: split this sort of docker-related functionality out into a separate class