Description of problem:
In ocp35 we can configure PodNodeSelector admission controller in master-config.yaml like below:
admissionConfig:
  pluginConfig:
    PodNodeSelector:
      location: admission-control-config-file.cfg
# cat admission-control-config-file.cfg
podNodeSelectorPluginConfig:
 clusterDefaultNodeSelector: region=west

But now in ocp36(v3.6.74), this failed with error: "start_master.go:112] Object 'Kind' is missing in '{"podNodeSelectorPluginConfig":{"clusterDefaultNodeSelector":"region=west"}}'"
I notice there is a pr to support versioned configuration: https://github.com/kubernetes/kubernetes/pull/39109

According to the new file type, I try to configure like:
apiVersion: apiserver.k8s.io/v1alpha1
kind: AdmissionConfiguration
plugins:
- name: "PodNodeSelector:"
  configuration:
    apiVersion: podnodeselector.admission.k8s.io/v1alpha1
    kind: Configuration
    podNodeSelectorPluginConfig:
      clusterDefaultNodeSelector: region=west

or

apiVersion: apiserver.k8s.io/v1alpha1
kind: AdmissionConfiguration
plugins:
- name: "PodNodeSelector:"
  configuration:
    apiVersion: podnodeselector.admission.k8s.io/v1alpha1
    kind: Configuration
    clusterDefaultNodeSelector: region=west

But both I get another error: start_master.go:112] no kind "AdmissionConfiguration" is registered for version "apiserver.k8s.io/v1alpha1"

Version-Release number of selected component (if applicable):
openshift v3.6.74
kubernetes v1.6.1+5115d708d7
etcd 3.1.0

How reproducible:
Always


Steps to Reproduce:
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Actual results:


Expected results:


Additional info: