exit 1 if -extended_metrics is not supported
exit 1 if -extended_metrics is not supported

https://github.com/mackerelio/mackerel-agent-plugins/pull/738#discussion_r590913790

mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins