Add virtio data plane support for qemu/kvm

QEMU 1.4 includes an experimental feature for high-performance disk I/O called virtio-blk data plane, It extends
QEMU to perform disk I/O in a dedicated thread that is optimized for I/O performance. IBM and Red Hat have published a whitepaper presenting the highest IOPS achieved to date under virtualization using virtio-blk data plane. It also is a available
as a Technology Preview in RedHat 7.0 Linux.

http://blog.vmsplice.net/2013/03/new-in-qemu-14-high-performance-virtio.html
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/7.0_Release_Notes/chap-Red_Hat_Enterprise_Linux-7.0_Release_Notes-Virtualization.html