feature request: support RestartPolicy

[iamnoah]

My thinking is for a Job, I might have a service that is a little bit unreliable, e.g., it becomes unhealthy and restarts from time to time, or restarts whenever a dependency is not ready.

So if I could specify KUBEXIT_RESTART_POLICY: Always/OnFailure/Never(default) and have the process restart as long as no death dependencies have terminated, that would make using somewhat fragile services in a Job much easier.