Exit enable mode.

def exit_enable_mode(self, exit_command="exit"):
        """Exit enable mode."""
        delay_factor = self.select_delay_factor(delay_factor=0)
        output = ""
        if self.check_enable_mode():
            self.write_channel(self.normalize_cmd(exit_command))
            time.sleep(0.3 * delay_factor)
            self.set_base_prompt()
            if self.check_enable_mode():
                raise ValueError("Failed to exit enable mode.")
        return output