Description of problem:
Standalone deployment failed to swap registry backend storage for a GlusterFS volume.

Version-Release number of the following components:
openshift-ansible-3.7.14-1.git.0.4b35b2d.el7
ansible-2.4.1.0-1.el7

How reproducible:
100%

Steps to Reproduce:
1. Run installation playbook to deploy an OCP cluster
# ansible-playbook -i hosts -vv /usr/share/ansible/openshift-ansible/playbooks/byo/config.yml
... playbook succeed...
2. Run standalone deployment playbook to deploy CNS at the existing OCP cluster, as registry backend storage.
# cat hosts
...
[OSEv3:children]
masters
nodes
etcd
glusterfs_registry
[OSEv3:vars]
...
openshift_hosted_registry_storage_kind=glusterfs
openshift_hosted_registry_storage_glusterfs_swap=true
...
[nodes]
glusterfs-1.example.com
glusterfs-2.example.com
glusterfs-3.example.com
...
[glusterfs_registry]
glusterfs-1.example.com  glusterfs_devices="['/dev/vsda']"
glusterfs-2.example.com  glusterfs_devices="['/dev/vsda']"
glusterfs-3.example.com  glusterfs_devices="['/dev/vsda']"
...
# ansible-playbook -i hosts -vv /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-glusterfs/registry.yml
...playbook succeed too...
3.

Actual results:
# oc describe pvc registry-glusterfs-claim
Name:		registry-glusterfs-claim
Namespace:	default
StorageClass:	standard
Status:		Pending
Volume:		
Labels:		<none>
Annotations:	volume.beta.kubernetes.io/storage-provisioner=kubernetes.io/gce-pd
Capacity:	
Access Modes:	
Events:
  FirstSeen	LastSeen	Count	From				SubObjectPath	Type		Reason			Message
  ---------	--------	-----	----				-------------	--------	------			-------
  1m		8s		8	persistentvolume-controller			Warning		ProvisioningFailed	Failed to provision volume with StorageClass "standard": invalid AccessModes [ReadWriteMany]: only AccessModes [ReadWriteOnce ReadOnlyMany] are supported


Expected results:
PVC should be bounding.

Additional info:
Installer create default storage class because environment is on GCP with cloud provider configuration. Seems related.
# oc get sc 
NAME                 TYPE
standard (default)   kubernetes.io/gce-pd   
# oc get pv 
NAME                                       CAPACITY   ACCESSMODES   RECLAIMPOLICY   STATUS      CLAIM                                   STORAGECLASS   REASON    AGE
pvc-40ea35d0-de50-11e7-895b-42010af0001b   1Gi        RWO           Delete          Bound       openshift-ansible-service-broker/etcd   standard                 47m
registry-glusterfs-volume                  5Gi        RWX           Retain          Available                                                                    35m
registry-volume                            5Gi        RWX           Retain          Available                                                                    35m
# oc get pvc 
NAME                       STATUS    VOLUME    CAPACITY   ACCESSMODES   STORAGECLASS   AGE
registry-claim             Pending                                      standard       35m
registry-glusterfs-claim   Pending                                      standard       35m

# oc get po -n glusterfs
NAME                                           READY     STATUS    RESTARTS   AGE
glusterblock-registry-provisioner-dc-1-jp58v   1/1       Running   0          54m
glusterfs-registry-b5f6r                       1/1       Running   0          59m
glusterfs-registry-fsls7                       1/1       Running   0          59m
glusterfs-registry-tx742                       1/1       Running   0          59m
heketi-registry-1-h56pz                        1/1       Running   0          55m