fix clone_disk with formats other than raw/qcow2

fix clone_disk with formats other than raw/qcow2

with commit 64d1a6a it's now possible to specify a format other than raw
or qcow2 when creating VMs. This can lead to an error when cloning the
VMs and a cloudinit disk with a different format is attached (e.g.
vmdk).

We use QEMU_FORMAT_RE in drive_is_cloudinit and according to the
QEMU_FORMAT_RE we support 7 different formats.

With this change we add any format other than 'raw' as '.<format>' to the
name and no longer die on any other format. Cloudinit disks with invalid
format are not cloned as the drive is recognized as cdrom, not cloudinit.

Signed-off-by: Mira Limbeck <m.limbeck@proxmox.com>