Shrink cloud image

Mail from: https://github.com/patrakov

Also regarding the disk size: the recent change of the default disk size to 20GB is OK for the use in on-premise virtual machines, but not really OK for the cloud, because of the extra billing charges for the unused space. Maybe we should create a big "vm" image and a small "cloud" image, and hope that the cloud provider and cloud-init will co-operate and resize the disk and the filesystem as requested? That definitely works with the image from linuximages.de.