This allows one to manage the checkpoints by using the `ctr image`
command.
The image is created with label "containerd.io/checkpoint". By
default, it is not included in the output of `ctr images ls`.
We can list the images by using the following command:
$ ctr images ls labels.containerd.\"io/checkpoint\"==true
Fixes#1026
Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
abbec62620