Add sleep and random exit image for e2e test

[ScorpioCPH]

Hi, this PR add an image for e2e test:

• Run a script that sleep a random seconds.
• Then exit a random code:
  • Exit 0 means this pod is succeeded.
  • Exit nonzero means this pod is failed.

We can use this image to count active/failed/succeeded pods.

@jlewi @gaocegege PTAL, thanks!

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This change is 

[ScorpioCPH]

/assign @gaocegege

[coveralls]

Coverage remained the same at 60.668% when pulling b06ff7e on ScorpioCPH:v1alpha2-e2e-test into e6d3c73 on kubeflow:v1alpha2.

[gaocegege]

/lgtm

[k8s-ci-robot]

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