Description of problem:
Block volumeMode PVC prebound a Block volumeMode PV, but with different accessMode bound successfully.

Version-Release number of selected component (if applicable):
oc v3.9.0-0.20.0
openshift v3.9.0-0.20.0
kubernetes v1.9.1+a0ce1bc657


How reproducible:
Always

Steps to Reproduce:
1. Create a Block volumeMode PV with accessMode ReadWriteOnce
2. Create a Block volumeMode PVC prebound the PV created above with accessMode ReadWriteMany
3. Check the PVC and PV

Actual results:
PVC is bound to PV

Expected results:
PVC is not bound to PV

Additional info:
When PVC is not prebound to PV, PVC will not be bound to PV.

# cat pv-block.yaml 
apiVersion: v1
kind: PersistentVolume
metadata:
  name: block-pv
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  volumeMode: Block
  persistentVolumeReclaimPolicy: Retain
  fc:
    targetWWNs: ["500a0981891b8dc5", "500a0981991b8dc5"]
    lun: 2
    readOnly: false

# cat pvc-block.json 
{
    "apiVersion": "v1",
    "kind": "PersistentVolumeClaim",
    "metadata": {
        "name": "claim-block"
    },
    "spec": {
        "accessModes": [ "ReadWriteMany" ],
        "volumeMode" : "Block",
        "volumeName" : "block-pv",
        "resources": {
            "requests": {
                "storage": "5Gi"
            }
        }
    }
}

# oc get pvc
NAME          STATUS    VOLUME     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
claim-block   Bound     block-pv   5Gi        RWO                           1m

# oc get pvc -o yaml
apiVersion: v1
items:
- apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    annotations:
      pv.kubernetes.io/bind-completed: "yes"
    creationTimestamp: 2018-01-17T01:55:48Z
    name: claim-block
    namespace: piqin
    resourceVersion: "63560"
    selfLink: /api/v1/namespaces/piqin/persistentvolumeclaims/claim-block
    uid: 89bafef7-fb29-11e7-8435-9457a56bf834
  spec:
    accessModes:
    - ReadWriteMany
    resources:
      requests:
        storage: 5Gi
    volumeMode: Block
    volumeName: block-pv
  status:
    accessModes:
    - ReadWriteOnce
    capacity:
      storage: 5Gi
    phase: Bound
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""