[Feature request] Support virtio block devices

[Daniele Lacamera]

To increase performance on virtual disk access, provide an option for each block device to pass it as virtio device at KVM startup.

For more information, check http://www.linux-kvm.org/page/Boot_from_virtio_block_device

In particular, we should look into an option that replaces -hda=file with -drive=file,if=virtio

It is perhaps possible to maintain the same disk order, or specify a name for each block device passed this way to KVM

[Daniele Lacamera (o-root-danielinux-net)]

r366 contains an experimental fix. To be checked whether second image is detected.

[Daniele Lacamera (o-root-danielinux-net)]

r367 contains a valid fix.