Enable MFA Device for user.

def enable_mfa_device(self,
                          user_name,
                          serial_number,
                          authentication_code_1,
                          authentication_code_2):
        """Enable MFA Device for user."""
        user = self.get_user(user_name)
        if serial_number in user.mfa_devices:
            raise IAMConflictException(
                "EntityAlreadyExists",
                "Device {0} already exists".format(serial_number)
            )

        user.enable_mfa_device(
            serial_number,
            authentication_code_1,
            authentication_code_2
        )