Add a method to identify running daemons in the process table

Summary: Ref T2374. Basically, sometimes we lose track of daemons and users get weird behaviors as a result. It's hard to figure out what's causing us to lose track of daemons since it rarely/never repros, but very easy to add some fallback code which does sanity checks against the process table. This should make the condition easy to understand/resolve until we eventually isolate and fix the pidfile stuff, or understand it better, or whatever.

Test Plan:
Ran the method and got reasonable output:

{F40173}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2374

Differential Revision: https://secure.phabricator.com/D5663