ctr --rootfs-propagation

A new flag --rootfs-propagation is added to ctr run and ctr container create to set propagation of the container rootfs.
Its value can be one of the propagation settings lists in Configuare bind propagation.

If the flag is set, say "rshared", users can check settings through ctr c info CONTAINER, and get the output below.

{
    "Spec": {
        "linux": {
            "rootfsPropagation": "rshared"
        }
    }
}