kubecontainer: add image ref to ImageService interfaces

pkg/kubelet/container/runtime.go

@@ -146,10 +146,10 @@ type IndirectStreamingRuntime interface {
 
 type ImageService interface {
 	// PullImage pulls an image from the network to local storage using the supplied
-	// secrets if necessary.
-	PullImage(image ImageSpec, pullSecrets []v1.Secret) error
+	// secrets if necessary. It returns a reference (digest or ID) to the pulled image.
+	PullImage(image ImageSpec, pullSecrets []v1.Secret) (string, error)
 	// IsImagePresent checks whether the container image is already in the local storage.
-	IsImagePresent(image ImageSpec) (bool, error)
+	IsImagePresent(image ImageSpec) (string, error)
 	// Gets all images currently on the machine.
 	ListImages() ([]Image, error)
 	// Removes the specified image.

pkg/kubelet/container/testing/fake_runtime.go

@@ -348,25 +348,25 @@ func (f *FakeRuntime) GetContainerLogs(pod *v1.Pod, containerID ContainerID, log
 	return f.Err
 }
 
-func (f *FakeRuntime) PullImage(image ImageSpec, pullSecrets []v1.Secret) error {
+func (f *FakeRuntime) PullImage(image ImageSpec, pullSecrets []v1.Secret) (string, error) {
 	f.Lock()
 	defer f.Unlock()
 
 	f.CalledFunctions = append(f.CalledFunctions, "PullImage")
-	return f.Err
+	return image.Image, f.Err
 }
 
-func (f *FakeRuntime) IsImagePresent(image ImageSpec) (bool, error) {
+func (f *FakeRuntime) IsImagePresent(image ImageSpec) (string, error) {
 	f.Lock()
 	defer f.Unlock()
 
 	f.CalledFunctions = append(f.CalledFunctions, "IsImagePresent")
 	for _, i := range f.ImageList {
 		if i.ID == image.Image {
-			return true, nil
+			return i.ID, nil
 		}
 	}
-	return false, f.InspectErr
+	return "", f.InspectErr
 }
 
 func (f *FakeRuntime) ListImages() ([]Image, error) {

pkg/kubelet/container/testing/runtime_mock.go

@@ -105,14 +105,14 @@ func (r *Mock) GetContainerLogs(pod *v1.Pod, containerID ContainerID, logOptions
 	return args.Error(0)
 }
 
-func (r *Mock) PullImage(image ImageSpec, pullSecrets []v1.Secret) error {
+func (r *Mock) PullImage(image ImageSpec, pullSecrets []v1.Secret) (string, error) {
 	args := r.Called(image, pullSecrets)
-	return args.Error(0)
+	return image.Image, args.Error(0)
 }
 
-func (r *Mock) IsImagePresent(image ImageSpec) (bool, error) {
+func (r *Mock) IsImagePresent(image ImageSpec) (string, error) {
 	args := r.Called(image)
-	return args.Get(0).(bool), args.Error(1)
+	return args.Get(0).(string), args.Error(1)
 }
 
 func (r *Mock) ListImages() ([]Image, error) {