Create an index on harbormaster_buildlog to reduce page load times

Summary: Resolves T5895.  This reduces page load times significantly when looking at builds.

Test Plan: Viewed a build, saw the page load a lot faster.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5895

Differential Revision: https://secure.phabricator.com/D10286

resources/sql/autopatches/20140818.harbormasterindex.1.sql

@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_harbormaster.harbormaster_buildlog
+  ADD KEY `key_buildtarget` (buildTargetPHID);