Automatic merge from submit-queue
Kubelet: add image ref to ImageService interfaces
This PR adds image ref (digest or ID, depending on runtime) to PullImage result, and pass image ref in CreateContainer instead of image name. It also
* Adds image ref to CRI's PullImageResponse
* Updates related image puller
* Updates related testing utilities
~~One remaining issue is: it breaks some e2e tests because they [checks image repoTags](https://github.com/kubernetes/kubernetes/blob/master/test/e2e/framework/util.go#L1941) while docker always returns digest in this PR. Should we update e2e test or continue to return repoTags in `containerStatuses.image`?~~
Fixes#38833.
This allows runtimes in different packages (dockertools, rkt, kuberuntime) to
share the same logic. Before this change, only dockertools support this
feature. Now all three packages support image pull throttling.