Use exponential backoff when getting the workflow status. (#170)
Use exponential backoff when getting the workflow status. (#170)

* We were using a fixed retry window that was too short O(5 seconds).
* Use exponential backoff and retry for up to 3 minutes. We are seeing
  test flakes due to problems getting the workflow status.

* Related to #169
kubeflow/testing,kubeflow/testing,kubeflow/testing,kubeflow/testing,kubeflow/testing