Every so often, ask the Aphict server how things are going
Summary: Ref T12573. This sends a "ping" to the server, and a "pong" back to the client, every 15 seconds. This tricks ELBs into thinking we're doing something useful and productive.
Test Plan: Ran bin/aphlict debug, loaded Phabricator, saw ping/pong in logs.
Reviewed By: chad
Maniphest Tasks: T12573
Differential Revision: https://secure.phabricator.com/D17717