watchman: migrate final watchman::Future -> folly::Future
watchman: migrate final watchman::Future -> folly::Future

Summary: selectWinner -> collectAny

Reviewed By: strager

Differential Revision: D13754361

fbshipit-source-id: cbee69d50835c2eb8ec51ed362a8da712910ddc0

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