Tear down the virtual box machine

def tear_down(self):
        """Tear down the virtual box machine
        """

        if not self.browser_config.get('terminate'):
            self.warning_log("Skipping terminate")
            return

        self.info_log("Tearing down")

        if self.browser_config.get('platform').lower() == 'linux':
            self.execute_command("shutdown -h now", username='root')

        elif self.browser_config.get('platform').lower() == 'windows':
            self.session.console.power_down()