Convert garden-o-matic guts over to promises where appropriate

Tools/GardeningServer/scripts/rollbot_unittests.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 144 matching lines @@
 };
 
 asyncTest("fetchCurrentRoll", 6, function() {
     var simulator = new NetworkSimulator();
     simulator.json = function(url)
     {
         return Promise.resolve(kSearchResults);
     };
 
     simulator.runTest(function() {
-        rollbot.fetchCurrentRoll(function(roll) {
+        rollbot.fetchCurrentRoll().then(function(roll) {
             equals(roll.issue, 16337011);
             equals(roll.url, "https://codereview.chromium.org/16337011");
             equals(roll.isStopped, false);
             equals(roll.fromRevision, "151668");
             equals(roll.toRevision, "151677");
         });
     }).then(start);
 });
 
 test("_isRollbotStopped", 1, function() {
     equals(true, rollbot._isRollbotStopped(kStoppedIssue));
 });
 
 })();