fix drive-mirror completion with cloudinit

fix drive-mirror completion with cloudinit

On clone_vm when cloning the disks while the VM is running, we use
drive-mirror. We skip completion until the last disk, but with a
cloudinit disk there's no drive-mirror and so no completion done. If it
is the last disk in the hash, we never complete the drive-mirror jobs
and no further cloning is possible as there are already active jobs
using the disks.

To fix it we have to call qemu_drive_mirror_monitor directly in the case
of cloudinit when completion is requested and there are jobs defined.

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