'Deactivate and detach MFA Device from user if device exists.'

def deactivate_mfa_device(self, user_name, serial_number):

    user = self.get_user(user_name)
    if (serial_number not in user.mfa_devices):
        raise IAMNotFoundException(u'Device    {0}    not    found'.format(serial_number))
    user.deactivate_mfa_device(serial_number)
