Add E2E jobs against AWS CI

[Jeffwan]

Community is asking different WG to own their infra and community won't provide a common shared testing infra anymore. Sees kubeflow/testing#752 for more details.

Pytorch migration works well and here's the PR to update test case to work on AWS Prow+ Argo cluster.
kubeflow/pytorch-operator#305

Xgboost presubmit is a little bit different from tensorflow and pyTorch, it only builds the image and doesn't create cluster resources. If there's plan to add e2e tests like create cluster -> run jobs -> tear down cluster. We can follow process in kubeflow/pytorch-operator#305.

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