move /ping and /status to /_monitor/ping and /_monitor/status

cc @ceejbot @bcoe @rockbot 

This aligns newww with docs and partners.

https://docs.npmjs.com/_monitor/ping
https://docs.npmjs.com/_monitor/status

https://parnters.npmjs.com/_monitor/ping
https://parnters.npmjs.com/_monitor/status