Clean up test folder before testing

[Jeffwan]

I tried to restart the post submit workflow to rebuild the image. However, I notice we didn't check folder existence and this results in failure.

https://argo.kubeflow-testing.com/workflows/kubeflow-test-infra/kubeflow-tf-operator-postsubmit-v1-e0b872e-2128-8fc4-dc8vm?tab=workflow&nodeId=kubeflow-tf-operator-postsubmit-v1-e0b872e-2128-8fc4-dc8vm-922790636&sidePanel=logs%3Akubeflow-tf-operator-postsubmit-v1-e0b872e-2128-8fc4-dc8vm-922790636%3Amain

The problem is we can not use latest commit id to publish manifest because there's no corresponding image tag built.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.