Do not persist SelfLink into etcd storage
Do not persist SelfLink into etcd storage

This behavior regressed in an earlier release. Clearing the self link
ensures that a new version is always written and reduces the size of the
stored object by a small amount. Add tests to verify that Create and
Update result in no SelfLink stored in etcd.

Kubernetes-commit: 461c3701f0915acbf49c339f5321fa86879a963e

kubernetes/apiextensions-apiserver,kubernetes/apiextensions-apiserver