Call $linter->setEngine in linter tests

Summary: We aren't calling `$linter->setEngine($engine)`, even though we do have an `$engine`. This causes unit tests for any linters which require an engine to fail.

Test Plan: Ran the unit tests for a [[https://github.com/freelancer/flarc/blob/master/src/lint/linter/ArcanistDockerContainerLinterProxy.php | third-party linter]].

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D20515

src/lint/linter/__tests__/ArcanistLinterTestCase.php

@@ -114,6 +114,7 @@ abstract class ArcanistLinterTestCase extends PhutilTestCase {
       $path_name = idx($config, 'path', $path);
       $engine->setPaths(array($path_name));
 
+      $linter->setEngine($engine);
       $linter->addPath($path_name);
       $linter->addData($path_name, $data);