Prevent pv controller from forcefully overwrite provisioned volume name

This fix prevents the PV controller from forcefully overwriting the provisioned volume's name with the generated PV name.  Instead, it allows dynamic provisioner implementers to set the name of the volume to a value that they choose.

pkg/controller/volume/persistentvolume/pv_controller.go

@@ -1329,7 +1329,9 @@ func (ctrl *PersistentVolumeController) provisionClaimOperation(claimObj interfa
 	glog.V(3).Infof("volume %q for claim %q created", volume.Name, claimToClaimKey(claim))
 
 	// Create Kubernetes PV object for the volume.
-	volume.Name = pvName
+	if volume.Name == "" {
+		volume.Name = pvName
+	}
 	// Bind it to the claim
 	volume.Spec.ClaimRef = claimRef
 	volume.Status.Phase = v1.VolumeBound