message: Add build configs for TF integration builder.
  This builder will check out TF from Piper and Estimator from GitHub.
  It will then build Estimator pip from a pinned revision, and install
  the pip package. It will then run TF tests that depend on Estimator
  code.
diff: @@ -416,6 +416,7 @@ cuda_py_test(
  "multi_and_single_gpu",
  "no_oss", # http://b/119349471
  "no_pip",
  + "tf_integration_test",
  ],
  )
  @@ -429,6 +430,7 @@ cuda_py_test(
  "multi_and_single_gpu",
  "no_oss", # http://b/119349471
  "no_pip",
  + "tf_integration_test",
  ],
  )
  