Automatic merge from submit-queue (batch tested with PRs 50536, 50809, 50220, 50399, 50176)
Make admission plugin handle mutating spec of uninitialized pods
Address https://github.com/kubernetes/kubernetes/issues/47837#issuecomment-321323243.
Updated to handle mutating pod spec of uninitialized pods:
* InitialResources
* PodNodeSelector
* PodTolerationRestriction
* ServiceAccount
Doesn't change:
* NodeRestriction: this plugin only cares about the mirror pods created by nodes, and mirror pods are exempted from initializers, so no modification required
* PersistentVolumeLabel, DefaultStorageClass: It only cares about PersistentVolume. We can revisit when we relax its validation.
* InitialResource: deprecated according to https://github.com/kubernetes/kubernetes/issues/47837#issuecomment-321388879
821445e127