message: Fix exception catch string
  Summary: Exception string has changed, fix test to match.
  Test Plan: all tests ok
  Reviewers: georgep
diff: @@ -391,7 +391,10 @@ class InfeedOutfeedTest(test_util.TensorFlowTestCase):
  dataset = tu.create_single_increasing_dataset(10, shape=[4, 4])
  infeed_queue = ipu_infeed_queue.IPUInfeedQueue(dataset, next_feed_id())
  infeed_queue.initializer
  - with self.assertRaisesRegexp(ValueError, 'The `initializer` function can'):
  + with self.assertRaisesRegexp(
  + ValueError,
  + 'The IPUInfeedQueue `initializer` function can only be accessed once.'
  + ):
  infeed_queue.initializer
  def testTrainingLoopWithInfeed(self):
  