Move cri/streaming to k8s.io/kubelet staging repository

Container runtimes like CRI-O and containerd reuse the code by copying
it from Kubernetes. To have a single source of truth for the streaming
server we now move the already isolated implementation to the
k8s.io/kubelet staging repository. This way runtimes can re-use the code
without copying the parts.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

pkg/kubelet/server/server_websocket_test.go

@@ -29,7 +29,7 @@ import (
 	"golang.org/x/net/websocket"
 
 	"k8s.io/apimachinery/pkg/types"
-	"k8s.io/kubernetes/pkg/kubelet/cri/streaming/portforward"
+	"k8s.io/kubelet/pkg/cri/streaming/portforward"
 )
 
 const (