Attaches a network interface to an instance.

        :type network_interface_id: str
        :param network_interface_id: The ID of the network interface to attach.

        :type instance_id: str
        :param instance_id: The ID of the instance that will be attached
            to the network interface.

        :type device_index: int
        :param device_index: The index of the device for the network
            interface attachment on the instance.

def attach_network_interface(self, network_interface_id,
                                 instance_id, device_index):
        """
        Attaches a network interface to an instance.

        :type network_interface_id: str
        :param network_interface_id: The ID of the network interface to attach.

        :type instance_id: str
        :param instance_id: The ID of the instance that will be attached
            to the network interface.

        :type device_index: int
        :param device_index: The index of the device for the network
            interface attachment on the instance.
        """
        params = {'NetworkInterfaceId' : network_interface_id,
                  'InstanceId' : instance_id,
                  'Deviceindex' : device_index}
        return self.get_status('AttachNetworkInterface', params, verb='POST')