make version of ts_mon compatible with appengine

infra_libs/ts_mon/common/test/errors_test.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 unittest
 
-from infra_libs.ts_mon import errors
+try:
+  from infra_libs.ts_mon.common import errors
+except ImportError: # pragma: no cover
+  from common import errors
 
 
 class ErrorsTest(unittest.TestCase):
 
   def test_decreasing_value(self):
     with self.assertRaises(errors.MonitoringDecreasingValueError) as e:
       raise errors.MonitoringDecreasingValueError('test', 1, 0)
     str(e.exception)
 
   def test_duplicate_registration(self):
@@ skipping 28 matching lines @@
 
   def test_no_configured_monitor_flush(self):
     with self.assertRaises(errors.MonitoringNoConfiguredMonitorError) as e:
       raise errors.MonitoringNoConfiguredMonitorError(None)
     str(e.exception)
 
   def test_no_configured_target(self):
     with self.assertRaises(errors.MonitoringNoConfiguredTargetError) as e:
       raise errors.MonitoringNoConfiguredTargetError('test')
     str(e.exception)