Fix bug in dockershim to set sandbox id properly.

pkg/kubelet/dockershim/convert.go

@@ -56,8 +56,10 @@ func toRuntimeAPIContainer(c *dockertypes.Container) (*runtimeApi.Container, err
 		return nil, err
 	}
 	labels, annotations := extractLabels(c.Labels)
+	sandboxID := c.Labels[sandboxIDLabelKey]
 	return &runtimeApi.Container{
 		Id:           &c.ID,
+		PodSandboxId: &sandboxID,
 		Metadata:     metadata,
 		Image:        &runtimeApi.ImageSpec{Image: &c.Image},
 		ImageRef:     &c.ImageID,

pkg/kubelet/dockershim/docker_container_test.go

@@ -75,6 +75,7 @@ func TestListContainers(t *testing.T) {
 		expected = append([]*runtimeApi.Container{{
 			Metadata:     configs[i].Metadata,
 			Id:           &id,
+			PodSandboxId: &sandboxID,
 			State:        &state,
 			Image:        configs[i].Image,
 			ImageRef:     &imageRef,