Use write connection and transactions in SQL patches

Summary:
Patches often read from slaves (possibly stale data) and use that information to write on master.
It causes problems when applying more patches quickly after each other because data created in previous patch may not be replicated yet.

Test Plan:
  $ bin/storage upgrade

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4483

resources/sql/patches/131.migraterevisionquery.php

@@ -1,12 +1,13 @@
 <?php
 
 $table = new DifferentialRevision();
+$table->openTransaction();
+$table->beginReadLocking();
 $conn_w = $table->establishConnection('w');
 
 echo "Migrating revisions";
 do {
-  $revisions = id(new DifferentialRevision())
-    ->loadAllWhere('branchName IS NULL LIMIT 1000');
+  $revisions = $table->loadAllWhere('branchName IS NULL LIMIT 1000');
 
   foreach ($revisions as $revision) {
     echo ".";
@@ -28,4 +29,7 @@ do {
       $revision->getID());
   }
 } while (count($revisions) == 1000);
+
+$table->endReadLocking();
+$table->saveTransaction();
 echo "\nDone.\n";