"cleanPodPolicy: All" does not clean up launcher pod

In MPIJob spec.runPolicy.cleanPodPolicy, we can set "All" to clean up all pods after completion including the launcher pod. However, it seems it only cleans up worker pods, as you can see in this [code](https://github.com/kubeflow/mpi-operator/blob/master/pkg/controller/mpi_job_controller.go#L607-L615).

Using the official example [pi.yaml](https://github.com/kubeflow/mpi-operator/blob/master/examples/v2beta1/pi/pi.yaml), if you change "cleanPodPolicy: Running" to "cleanPodPolicy: All", you can reproduce the issue.

Start in pkg/controller/mpi_job_controller.go around lines 607-615, then reproduce the behavior with examples/v2beta1/pi/pi.yaml after changing cleanPodPolicy from Running to All. Trace the cleanup handling for worker and launcher pods. Done means cleanPodPolicy: All removes the launcher pod as well as the worker pods after completion.

Written by the indexing model from the issue text.