Change fsGroup to mounterArgs in volume.SetUp() to allow for future extension.

pkg/volume/fc/fc_test.go

@@ -179,7 +179,7 @@ func doTestPlugin(t *testing.T, spec *volume.Spec) {
 		t.Errorf("Unexpected path, expected %q, got: %q", expectedPath, path)
 	}
 
-	if err := mounter.SetUp(nil); err != nil {
+	if err := mounter.SetUp(volume.MounterArgs{}); err != nil {
 		t.Errorf("Expected success, got: %v", err)
 	}
 	if _, err := os.Stat(path); err != nil {