Return STDIN, STDOUT, and STDERR file descriptors from parent process

Summary:
Ref T13675. When a process daemonizes, it needs to close these actual file descriptors, so the calling context must provide them.

Elsewhere, modify the embedded "arc" to provide them. Then use them in place of reopening the streams.

Test Plan: Ran locally with embedded "arc", will deploy for production hangs.

Maniphest Tasks: T13675

Differential Revision: https://secure.phabricator.com/D21804