Before this patch, pull progress wouldn't show the `Extracting` layer
status which made the pull look like it got stuck when extracting a big
layer.
Use the `containerd.io/snapshot/cri.layer-digest` snapshot labels to
find a corresponding snapshot and check whether it's `active` or
`committed` to set the layer status accordingly.
Despite the `cri.` component in the label name, it's not CRI specific -
it only depends on the `snapshotters.AppendInfoHandlerWrapper`.
We _could_ also use the `Usage` snapshot method to query the exact
progress of the unpack, but it would be too expensive as the
implementation time complexity will be proportional to the snapshot size.
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>
96ef85272f