Update dependencies to use external-snapshotter v1.0.0-rc4

This PR updates dependencies to use external-snapshotter v1.0.0-rc4.
It also updates the controller code to use the new ReadyToUse field
in VolumeSnapshot status.

Gopkg.toml

@@ -38,7 +38,7 @@
 
 [[constraint]]
   name = "github.com/kubernetes-csi/external-snapshotter"
-  version = "1.0.0-rc3"
+  version = "1.0.0-rc4"
 
 [[constraint]]
   name = "github.com/kubernetes-sigs/sig-storage-lib-external-provisioner"

pkg/controller/controller.go

@@ -595,7 +595,7 @@ func (p *csiProvisioner) getVolumeContentSource(options controller.VolumeOptions
 	if err != nil {
 		return nil, fmt.Errorf("error getting snapshot %s from api server: %v", options.PVC.Spec.DataSource.Name, err)
 	}
-	if snapshotObj.Status.Ready == false {
+	if snapshotObj.Status.ReadyToUse == false {
 		return nil, fmt.Errorf("snapshot %s is not Ready", options.PVC.Spec.DataSource.Name)
 	}
 

pkg/controller/controller_test.go

@@ -1290,7 +1290,7 @@ func newSnapshot(name, className, boundToContent, snapshotUID, claimName string,
 		},
 		Status: crdv1.VolumeSnapshotStatus{
 			CreationTime: creationTime,
-			Ready:        ready,
+			ReadyToUse:   ready,
 			Error:        err,
 			RestoreSize:  size,
 		},