Description of problem:
you can define multiple storage classes as default
es:

[rspazzol@rspazzol F5]$ oc get storageclass
NAME                          TYPE
iscsi (default)               iscsi           
local-pod-default (default)   local-pod/nfs  

How reproducible:
100%

Steps to Reproduce:
define multiple storage classes as default

Actual results:
multiple storage classes are defined as default (unknown system behavior when a pvc is actually created)


Expected results:
either an error message or that the default property is moved to the latest storage class that was defined as default.


StorageClass Dump (if StorageClass used by PV/PVC):

[rspazzol@rspazzol F5]$ oc get storageclass -o yaml
apiVersion: v1
items:
- apiVersion: storage.k8s.io/v1beta1
  kind: StorageClass
  metadata:
    annotations:
      storageclass.beta.kubernetes.io/is-default-class: "true"
    creationTimestamp: 2017-06-21T19:05:39Z
    name: iscsi
    namespace: ""
    resourceVersion: "404538"
    selfLink: /apis/storage.k8s.io/v1beta1/storageclasses/iscsi
    uid: 9d4974ce-56b4-11e7-89a7-fa163ea64764
  parameters:
    initiators: iqn.2003-03.com.raffa:master-0,iqn.2003-03.com.raffa:app-node-1,iqn.2003-03.com.raffa:app-node-0,iqn.2003-03.com.raffa:infranode-0
    iqn: iqn.2003-01.org.example.mach1:1234
    iscsiInterface: default
    targetPortal: 192.168.80.110:3260
    volumeGroup: vg-targetd
  provisioner: iscsi
- apiVersion: storage.k8s.io/v1beta1
  kind: StorageClass
  metadata:
    annotations:
      storageclass.beta.kubernetes.io/is-default-class: "true"
    creationTimestamp: 2017-06-17T04:09:54Z
    name: local-pod-default
    namespace: ""
    resourceVersion: "109385"
    selfLink: /apis/storage.k8s.io/v1beta1/storageclasses/local-pod-default
    uid: d11ea492-5312-11e7-89a7-fa163ea64764
  provisioner: local-pod/nfs
kind: List
metadata: {}
resourceVersion: ""
selfLink: ""