add a test for waitUntilReadyToQuery
add a test for waitUntilReadyToQuery

Summary:
Add a test that ensures waitUntilReadyToQuery does wait for the first
pass through the iothread loop.

Reviewed By: genevievehelsel

Differential Revision: D32228177

fbshipit-source-id: b5836d67a711705874f560c00a831e68968922d0

facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,facebook/watchman,facebook/watchman