In almost all cases, there already is an expected format. Allow
setting a special value 'auto-detect' to opt-in to automatic format
detection by 'qemu-img' for the exceptions.
Suggested-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
936fbe3f35