Reset Drydock git working copies better

Summary: Ref T9252. We're currently resetting to the local branch, but should be resetting to the origin branch.

Test Plan: Restarted a build, had it run `git show`, saw proper HEAD.

Reviewers: chad

Reviewed By: chad

Subscribers: hach-que

Maniphest Tasks: T9252

Differential Revision: https://secure.phabricator.com/D14194

Author: epriestley

src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php

@@ -213,7 +213,10 @@ public function activateLease(
         $cmd[] = 'git reset --hard %s';
         $arg[] = $commit;
       } else if ($branch !== null) {
-        $cmd[] = 'git reset --hard %s';
+        $cmd[] = 'git checkout %s';
+        $arg[] = $branch;
+
+        $cmd[] = 'git reset --hard origin/%s';
         $arg[] = $branch;
       } else {
         $cmd[] = 'git reset --hard HEAD';