Pass overseer configuration over stdin

Summary:
Ref T7352. This changes phd to pass configuration to overseers over stdin. We still run one overseer per daemon.

The "status" stuff needs some cleanup, but it's mostly just UI/cosmetic.

Test Plan:

• Ran phd debug, phd launch, phd start, phd status, phd stop, etc.
• Verified PID files write in a reasonable format.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7352

Differential Revision: https://secure.phabricator.com/D11855