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)
best to stop beforehand (as per docs)  - not sure if it is really required though... - Sven?