[Telemetry] Reduce misleading spam in unittest output.

tools/telemetry/telemetry/page/page_measurement_unittest.py

 # Copyright (c) 2012 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 json
 import os
 
 from telemetry import test
+from telemetry.core import exceptions
 from telemetry.core import wpr_modes
 from telemetry.page import page as page_module
 from telemetry.page import page_measurement
 from telemetry.page import page_measurement_unittest_base
 from telemetry.page import page_set
 from telemetry.page import page_set_archive_info
 from telemetry.unittest import options_for_unittests
 
 
 class MeasurementThatFails(page_measurement.PageMeasurement):
   def MeasurePage(self, page, tab, results):
-    raise page_measurement.MeasurementFailure('Intentional failure.')
+    raise exceptions.IntentionalException
 
 class MeasurementThatHasDefaults(page_measurement.PageMeasurement):
   def AddCommandLineArgs(self, parser):
     parser.add_option('-x', dest='x', default=3)
 
   def MeasurePage(self, page, tab, results):
     if not hasattr(self.options, 'x'):
       raise page_measurement.MeasurementFailure('Default option was not set.')
     if self.options.x != 3:
       raise page_measurement.MeasurementFailure(
@@ skipping 120 matching lines @@
       if os.path.isfile(test_archive):
         os.remove(test_archive)
 
   def testActions(self):
     ps = self.CreateEmptyPageSet()
     page = PageWithAction('file://blank.html', ps)
     ps.AddPage(page)
     measurement = MeasurementWithAction()
     self.RunMeasurement(measurement, ps, options=self._options)
     self.assertTrue(page.run_test_action_called)