Add argo workflow status link

[jose5918]

Reasons for change:

• Would like a link directly from a PR to the corresponding argo workflow to make debugging easier

Changes made:

• Adds steps to the workflow for setting github status to pending, success, or failure
• Adds github_status.py for sending status update

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This change is 

[k8s-ci-robot]

Hi @jose5918. Thanks for your PR.

I'm waiting for a kubernetes or tensorflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[coveralls]

Coverage remained the same at 31.746% when pulling fadc8ba on jose5918:argo-status into 0de450f on tensorflow:master.

[jose5918]

@jlewi Does this GIT_TOKEN have the ability to post status? I just used what was available when doing this

[gaocegege]

LGTM but I am not sure if we should place the code in this repo.

[gaocegege]

I think we could add a todo since we are migrating to kubeflow/tf-operator.

[jose5918]

@gaocegege Yeah, I can move most if not everything to kubeflow/testing, but I'm not where people want it. It might be easier to do an initial test as is in this repo just to see if it works though

[jlewi]

Generic code should be in kubeflow/testing.

Is there a way to avoid having to add the steps to each workflow? Can we move the logic into run_e2e_workflow.py?

[jose5918]

@jlewi Sure, I'll do that.

[jose5918]

Closing in favor of kubeflow/testing#17