Bust jest caching and fix tests

packager/react-packager/src/Cache/__mocks__/Cache.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+'use strict';
+
+class Cache {
+  get(filepath, field, cb) {
+    return cb(filepath);
+  }
+
+  invalidate(filepath) { }
+  end() { }
+}
+
+module.exports = Cache;