Suggest to update the imagePullPolicy to "IfNotPresent" for Pipeline component

[jinchihe]

Installed last version kubeflow, and found the pipeline has been installed by default together, That's great! But when I reinstall kubeflow for some reasons, I found the pipeline pod cannot be ready for long time. Checked the reason, that caused by downloading pipeline related image again.

Checked other component of kubeflow, the imagePullPolicy of most of component are "IfNotPresent", but the pipeline ones are "Always". so the image need to be download again, that wastes time.

So suggest to update imagePullPolicy to "IfNotPresent" for Pipeline component, so that user can re-deploy kubeflow quickly.

[jlewi]

Anyone interest in providing a PR?

[jinchihe]

@jlewi I have already created one PR to update this, Thanks. PR: #2251