Introduce nsenter writer for volume plugins

pkg/volume/iscsi/iscsi_test.go

@@ -244,7 +244,7 @@ func TestPersistentClaimReadOnlyFlag(t *testing.T) {
 	// readOnly bool is supplied by persistent-claim volume source when its builder creates other volumes
 	spec := volume.NewSpecFromPersistentVolume(pv, true)
 	pod := &api.Pod{ObjectMeta: api.ObjectMeta{UID: types.UID("poduid")}}
-	builder, _ := plug.NewBuilder(spec, pod, volume.VolumeOptions{}, nil)
+	builder, _ := plug.NewBuilder(spec, pod, volume.VolumeOptions{})
 
 	if !builder.IsReadOnly() {
 		t.Errorf("Expected true for builder.IsReadOnly")