Prevent double rendering of unit test results

Summary: D14037 had the logic slightly wrong and unit test results are now being double rendered.

Test Plan: Ran a unit test with arc unit -- path/to/test and saw the results rendered only once.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14495