Extend StandardStorage with Destroy to implement rbac storage destroy

staging/src/k8s.io/apiserver/pkg/registry/rest/rest.go

@@ -283,6 +283,11 @@ type StandardStorage interface {
 	GracefulDeleter
 	CollectionDeleter
 	Watcher
+
+	// Destroy cleans up its resources on shutdown.
+	// Destroy has to be implemented in thread-safe way and be prepared
+	// for being called more than once.
+	Destroy()
 }
 
 // Redirector know how to return a remote resource's location.