Fix failing tests by waiting for state assertions
Fix failing tests by waiting for state assertions

Summary:
Many of watchman's tests flush subscriptions in order to force notifications
to this client. Flush subscriptions ignores any asserted states and thus,
can cause results to be non-deterministic. Flush subscriptions introduces
the possibility that a subscription's query is run concurrently with a
source code operation.

Reviewed By: wez

Differential Revision: D6243050

fbshipit-source-id: 806e2ea15ff5182e7aa109b7be6fdec1a9a83c8b

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