make version of ts_mon compatible with appengine

infra_libs/ts_mon/test/stubs.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import mock
 
 from infra_libs.ts_mon import interface
 from infra_libs.ts_mon import monitors
-from infra_libs.ts_mon import targets
+from infra_libs.ts_mon.common import targets
 
 
 class MockState(interface.State):  # pragma: no cover
 
   def __init__(self):
     self.global_monitor = None
     self.default_target = None
     self.flush_mode = None
     self.flush_thread = None
     self.metrics = set()
@@ skipping 23 matching lines @@
     pass
 
   def flush(self):
     pass
 
   def register(self, metric):
     pass
 
   def unregister(self, metric):
     pass