* Move setup of libvirt disk cachemode into imagebackend module
* Ensure to use 'hdN' for IDE disk device in libvirt driver
* Don't hardcode use of 'virtio' for root disk in libvirt driver
* Move more libvirt disk setup into the imagebackend module
* Refactor libvirt imagebackend module to reduce code duplication
* Move libvirt disk config setup out of main get_guest_config method
* Don't set device='cdrom' for all disks in libvirt driver
* Get rid of pointless 'suffix' parameter in libvirt imagebackend