Add container modification API and cli.

docker modify CONTAINER device-add /device/path
docker modify CONTAINER device-remove /device/path

This patch will allow the user to add or remove a device to a running
container.

Co-Authored-By: Chris Alfonso <calfonso@redhat.com> (github: calfonso)
Docker-DCO-1.1-Signed-off-by: Ian Main <imain@redhat.com> (github: imain)
Requiring the device file be present to remove the device is great, because it prevents the insecure race conditiony behavior that I warned about in the previous PR :dancer: