fixup error messaging for timeout in cookie sync
fixup error messaging for timeout in cookie sync

Summary:
Since refactoring this to use the C++ condition_variable,
we've been reporting cookie sync timeouts as unknown errors.

Since we're using the predicate form of condition_variable::wait_until, a
failure is always a timeout, so let's adjust the how we log it.

Reviewed By: simpkins

Differential Revision: D5082053

fbshipit-source-id: d64f1a50d520b04a0064cea629072d335c8ced76

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