Use standard arguments to implement --trace in the overseer

Summary: Ref T3557. Currently, phd debug doesn't show events in the overseer, because it handles --trace specially. Use standard handling instead.

Test Plan: Ran phd debug and saw overseer events (like event dispatch and queries) logged.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3557

Differential Revision: https://secure.phabricator.com/D6540