Returns a list of vim.vm.device.VirtualDeviceSpec specifying to edit a
    deployed serial port configuration to the new given config

    serial_old_new
         Dictionary with old and new keys which contains the current and the
          next config for a serial port device

def _update_serial_ports(serial_old_new):
    '''
    Returns a list of vim.vm.device.VirtualDeviceSpec specifying to edit a
    deployed serial port configuration to the new given config

    serial_old_new
         Dictionary with old and new keys which contains the current and the
          next config for a serial port device
    '''
    serial_changes = []
    if serial_old_new:
        devs = [serial['old']['adapter'] for serial in serial_old_new]
        log.trace('Updating serial ports %s', devs)
        for item in serial_old_new:
            current_serial = item['old']
            next_serial = item['new']
            difference = recursive_diff(current_serial, next_serial)
            difference.ignore_unset_values = False
            if difference.changed():
                serial_changes.append(_apply_serial_port(next_serial,
                                                         current_serial['key'],
                                                         'edit'))
        return serial_changes