Add a convenience shell script for Docker container C/R

Since the command line for checkpointing and restoring Docker containers
is very long and there are some manual steps involved before restoring
a container, it's much easier to use a shell script to automate the work.

One would simply do:

$ sudo docker_cr.sh -c
$ sudo docker_cr.sh -r

Signed-off-by: Saied Kazemi <saied@google.com>
Acked-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>