Fixed spotty CanSupport for PV and added more unit tests for same

pkg/volume/rbd/rbd.go

@@ -53,7 +53,7 @@ func (plugin *RBDPlugin) Name() string {
 }
 
 func (plugin *RBDPlugin) CanSupport(spec *volume.Spec) bool {
-	if spec.VolumeSource.RBD == nil {
+	if spec.VolumeSource.RBD == nil && spec.PersistentVolumeSource.RBD == nil {
 		return false
 	}
 	// see if rbd is there

pkg/volume/rbd/rbd_test.go

@@ -37,6 +37,9 @@ func TestCanSupport(t *testing.T) {
 	if plug.Name() != "kubernetes.io/rbd" {
 		t.Errorf("Wrong name: %s", plug.Name())
 	}
+	if plug.CanSupport(&volume.Spec{Name: "foo", VolumeSource: api.VolumeSource{}}) {
+		t.Errorf("Expected false")
+	}
 }
 
 type fakeDiskManager struct{}