Add a missing artifactIndex key to HarbormasterBuildArtifact

Summary: See PHI176. We issue a query with only `artifactIndex` from `BuildTarget`, but don't have an applicable key.

Test Plan: This isn't on the normal Harbormaster execution path so I'm not 100% sure I have a local repro, but will confirm with customer.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Differential Revision: https://secure.phabricator.com/D18732

src/applications/harbormaster/storage/build/HarbormasterBuildArtifact.php

@@ -43,6 +43,9 @@ final class HarbormasterBuildArtifact extends HarbormasterDAO
         'key_target' => array(
           'columns' => array('buildTargetPHID', 'artifactType'),
         ),
+        'key_index' => array(
+          'columns' => array('artifactIndex'),
+        ),
       ),
     ) + parent::getConfiguration();
   }