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