informer: fix race against Run and SetTransform/SetWatchErrorHandler

`SetWatchErrorHandler` claims it will fail if Run() has already started.
But if they are called concurrently, it will actually trigger a data
race.

With this PR:
```
62702 runs so far, 0 failures (100.00% pass rate). 59.152682ms avg, 189.068387ms max, 26.623785ms min
```

Without this PR:
```
5012 runs so far, 38 failures (99.25% pass rate). 58.675502ms avg, 186.018084ms max, 29.468104ms min
```

Kubernetes-commit: 35d2431b3a89c5bd693846952e9d27ce4e3a0754

tools/cache/shared_informer.go

@@ -459,29 +459,30 @@ func (s *sharedIndexInformer) Run(stopCh <-chan struct{}) {
 		klog.Warningf("The sharedIndexInformer has started, run more than once is not allowed")
 		return
 	}
-	fifo := NewDeltaFIFOWithOptions(DeltaFIFOOptions{
-		KnownObjects:          s.indexer,
-		EmitDeltaTypeReplaced: true,
-		Transformer:           s.transform,
-	})
-
-	cfg := &Config{
-		Queue:             fifo,
-		ListerWatcher:     s.listerWatcher,
-		ObjectType:        s.objectType,
-		ObjectDescription: s.objectDescription,
-		FullResyncPeriod:  s.resyncCheckPeriod,
-		RetryOnError:      false,
-		ShouldResync:      s.processor.shouldResync,
-
-		Process:           s.HandleDeltas,
-		WatchErrorHandler: s.watchErrorHandler,
-	}
 
 	func() {
 		s.startedLock.Lock()
 		defer s.startedLock.Unlock()
 
+		fifo := NewDeltaFIFOWithOptions(DeltaFIFOOptions{
+			KnownObjects:          s.indexer,
+			EmitDeltaTypeReplaced: true,
+			Transformer:           s.transform,
+		})
+
+		cfg := &Config{
+			Queue:             fifo,
+			ListerWatcher:     s.listerWatcher,
+			ObjectType:        s.objectType,
+			ObjectDescription: s.objectDescription,
+			FullResyncPeriod:  s.resyncCheckPeriod,
+			RetryOnError:      false,
+			ShouldResync:      s.processor.shouldResync,
+
+			Process:           s.HandleDeltas,
+			WatchErrorHandler: s.watchErrorHandler,
+		}
+
 		s.controller = New(cfg)
 		s.controller.(*controller).clock = s.clock
 		s.started = true