Initial attempt for dist format support
Completed initial support for creating disks with qcow2 format as unmanaged storage

libvirt or virt-install only allows to create qcow2 images if those are
assigned to a libvirt storage pool.
Fix description of disks_format parameter

was copy&paste from virt_disks parameter
Merge pull request #1 from TelekomCloud/disks_format

Introduce support to create "unmanaged" disks with a qcow2 or other image format