Launch daemons with a full Phabricator environment in the overseers

Summary:
Ref T1670. Prepare for the overseers to talk directly to the database instead of using Conduit. See T1670 for discussion.

This shouldn't impact anything, except it has a very small chance of destabilizing the overseers.

Test Plan:
Ran `phd launch`, `phd debug`, `phd start`.

Ran with `--trace-memory` and verified elevated but mostly steady memory usage (8MB / overseer). This climbed by 0.05KB / sec (4MB / day) but the source of the leaks seems to be the cURL calls we're making over Conduit so this will actually fix that. Disabling `--conduit-uri` reported steady memory usage. I wasn't able to identify anything leaking within code we control. This may be something like a dynamic but capped buffer in cURL, since we haven't seen any issues in the wild.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1670

Differential Revision: https://secure.phabricator.com/D6534