more de-flaking of wm_wait.py
more de-flaking of wm_wait.py

Summary: one more thing to wait on

Differential Revision: D7160742

fbshipit-source-id: 5b7faaaae78bea5246c39031e677329262e509e3

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