R1:9b843a3d441e

Allow linking unit tests

Summary:
We have lots of info about unit tests.
This allows linking them from Unit field.

Test Plan: Monkey patched `$test['link']`, clicked on it.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3434