R1:bcdb7e9a2c69

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