message: Fix ipu_ops test
  Test Plan: ipu_ops now passes
  Reviewers: davidn
diff: @@ -50,9 +50,9 @@ class ContribIpuOpsTest(test_util.TensorFlowTestCase):
  result = sess.run(out, fd)
  self.assertAllClose(result, [3.0])
  - # Event trace (1x compile, 1x load engine, 1x execute)
  + # 1x compile begin, 1x compile end, 1x load engine, 1x execute
  e = sess.run(events)
  - self.assertEqual(len(e), 3)
  + self.assertEqual(len(e), 4)
  dump = tf.contrib.ipu.utils.extract_all_strings_from_event_trace(e);
  self.assertTrue(len(dump) > 100)
  