Upgrade the image - preserving machine state

Stop the VM, download, and restart (preserve machine state - ie if it was running before, it will be running after upgraded).

Docker-DCO-1.1-Signed-off-by: Michael Neale michael.neale@gmail.com (github: michaelneale)
Isn't it valid to download _before_ we stop, or do we have to stop the machine before we can update the ISO?