[watchman] catch connection closed exception
[watchman] catch connection closed exception

Summary: when we're waiting for events from watchman, we do this `blocking_read`. it (rarely) gets an exception because the `wait_read` is called on an already-closed file descriptor.

Reviewed By: nmote

Differential Revision: D28021281

fbshipit-source-id: 07313045d73e255c3ef7bbec14d1018250a37e64

mroch/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow