Run a commit discovery daemon only once

Summary:
Discover commits then return; useful when initializing new repositories
in unit tests.

By which I mean "when initializing a new repository in my unit test that
I'm working on".

Test Plan: Using this in a PhabricatorTestCase.

Reviewers: epriestley, aran

Reviewed By: epriestley

CC: aran, edward, epriestley

Differential Revision: 948

src/applications/repository/daemon/commitdiscovery/base/PhabricatorRepositoryCommitDiscoveryDaemon.php

@@ -36,6 +36,11 @@ abstract class PhabricatorRepositoryCommitDiscoveryDaemon
     }
   }
 
+  final public function runOnce() {
+    $this->repository = $this->loadRepository();
+    $this->discoverCommits();
+  }
+
   protected function isKnownCommit($target) {
     if (isset($this->commitCache[$target])) {
       return true;