def detach
      parent.with_open_session do |session|
        machine = session.machine

        machine.detach_device(storage_controller.name, port, device)
      end
    end
def detach
      parent.with_open_session do |session|
        machine = session.machine

        machine.detach_device(storage_controller.name, port, device)
      end
    end
Detaches the medium from it's parent virtual machine. Note that this
 **does not delete** the `medium` which this attachment references; it
 merely removes the assocation of said medium with this attachment's
 virtual machine.