Description of problem:
- When cluster has default storageclass, PVC created by oc set volume always bind to the default storage class. In ohter words, it cannot be bound to static PV.

Version-Release number of selected component (if applicable):
- OCP 3.9

  # oc version
  oc v3.9.14
  kubernetes v1.9.1+a0ce1bc657
  features: Basic-Auth GSSAPI Kerberos SPNEGO
   
  Server https://knakayam-ose39-all.example.com:8443
  openshift v3.9.14
  kubernetes v1.9.1+a0ce1bc657

How reproducible: 100%

Steps to Reproduce:
1. Prepare default StorageClass (dynamic in below) and staic PV(pv0001)

  # oc get sc
  NAME                PROVISIONER         AGE
  cephfs              ceph.com/cephfs     44d
  dynamic (default)   kubernetes.io/rbd   48d

  // Also, we prepare for static PV. (We would like to let PVC bind to this static PV.)
  # oc get pv
  NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM            STORAGECLASS   REASON    AGE
  pv0001                                     1Gi        RWX            Recycle          Available   default/claim1                            23s

2. Run oc set volumes without --claim-name.

  # oc set volumes dc/docker-registry --name=registry-storage --claim-name=registry-claim --claim-mode=ReadWriteMany --claim-size=1Gi --add
  persistentvolumeclaims/registry-claim

3. PVC created is alywas has "storageClassName: dynamic".

  # oc get pvc
  NAME             STATUS    VOLUME    CAPACITY   ACCESS MODES   STORAGECLASS   AGE
  registry-claim   Pending                                       dynamic        1m

  # oc get pvc registry-claim -o yaml |grep storageClassName
    storageClassName: dynamic

Actual results:
- Please refer to step-3 above. It always has "storageClassName: dynamic" so that it cannot bind to static PV(pv0001).

Expected results:
- Assign PVC created by oc set volume bind to static PV.

Additional info:
- If we can specify 'storageClassName: ""', then it is possible to use staic PV - ref: https://kubernetes.io/docs/concepts/storage/persistent-volumes/#class-1