Use the configuration driven unit test engine

Summary: Ref T5568. Use the very-new, very-beta ArcanistConfigurationDrivenUnitTestEngine unit test engine.

Test Plan: arc unit

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T5568

Differential Revision: https://secure.phabricator.com/D13853