message: Fix a replicate_model_fn_test that is dependent on the number of hardware GPUs.
  It has been causing failures when run on a machine with 4 GPUs.
diff: @@ -288,7 +288,7 @@ class ReplicateModelTest(test_util.TensorFlowTestCase):
  with self.test_session() as session:
  replicated_model_fn = replicate_model_fn.replicate_model_fn(
  - self.model_fn, self.optimizer_fn)
  + self.model_fn, self.optimizer_fn, devices=['/gpu:0'])
  estimator_spec = replicated_model_fn(
  features, labels, model_fn_lib.ModeKeys.TRAIN, self.params)
  session.run(variables.global_variables_initializer())
  