Add error handling for Register() call

Register() can return an error as [1], so this adds the error handling.

[1]: https://github.com/kubernetes/kubernetes/blob/f772c9017c16bbc983e59a19162814629a467cef/pkg/scheduler/framework/v1alpha1/registry.go#L56

Author: Kenichi Omichi

test/integration/scheduler/preemption_test.go

@@ -125,9 +125,12 @@ func TestPreemption(t *testing.T) {
 	// Initialize scheduler with a filter plugin.
 	var filter tokenFilter
 	registry := make(framework.Registry)
-	registry.Register(filterPluginName, func(_ *runtime.Unknown, fh framework.FrameworkHandle) (framework.Plugin, error) {
+	err := registry.Register(filterPluginName, func(_ *runtime.Unknown, fh framework.FrameworkHandle) (framework.Plugin, error) {
 		return &filter, nil
 	})
+	if err != nil {
+		t.Fatalf("Error registering a filter: %v", err)
+	}
 	plugins := &schedulerconfig.Plugins{
 		Filter: &schedulerconfig.PluginSet{
 			Enabled: []schedulerconfig.Plugin{