Fix controller problematic log output

Signed-off-by: Ming <mqiu@vmware.com>

pkg/util/kube/periodical_enqueue_source.go

@@ -18,6 +18,7 @@ package kube
 
 import (
 	"context"
+	"fmt"
 	"reflect"
 	"time"
 
@@ -96,3 +97,10 @@ func (p *PeriodicalEnqueueSource) Start(ctx context.Context, h handler.EventHand
 
 	return nil
 }
+
+func (p *PeriodicalEnqueueSource) String() string {
+	if p.objList != nil {
+		return fmt.Sprintf("kind source: %T", p.objList)
+	}
+	return "kind source: unknown type"
+}