Ordered cleanup with OwnerReference

The Memcached controller creates pods containing OwnerReferences in their metadata section. Referencing their owner ensures they will be deleted when the `memcached-sample` CR is deleted.

You can see the OwnerReference set on any of Memcached's pods:

kubectl get pods -o yaml | grep ownerReferences -A10

Delete the memcached-sample Custom Resource:

kubectl delete memcached memcached-sample

Thanks to OwnerReferences, all of the pods should be deleted. You can check with the familiar kubectl get pods.