text: Title: [Test] E2e Tests for Notebook Examples
  Body: ### What you would like to be added?
  
  We plan to add e2e tests for notebooks in CI/CD, run with papermill.
  
  REF: https://github.com/nteract/papermill
  
  The notebook examples in need of e2e tests are listed in the following table:
  
  Under `examples/v1beta1/kubeflow-pipelines`:
  
  - [ ] early-stopping.ipynb
  - [ ] kubeflow-e2e-mnist.ipynb
  
  Under `examples/v1beta1/sdk`:
  
  - [ ] cmaes-and-resume-policies.ipynb
  - [ ] nas-with-darts.ipynb
  - [ ] tune-train-from-func.ipynb
  
  And I would strongly recommend that we start with examples under `sdk` subdirectory since examples under `kubeflow-pipelines` need full kubeflow components on test env and are more difficult :)
  
  ### Why is this needed?
  
  This will help us ensure the correctness of our notebook examples for data scientists.
  
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