virtio support in Eucalyptus 2.0

Beginning with version 2.0, Eucalyptus will support KVM virtio as a configuration option. Virtio is a framework that brings paravirtualized device drivers to KVM similar to Xen's architecture. Paravirtualization should enhance I/O performance in comparison to a fully virtualized environment and help simplify the interaction between guest and hypervisor. Using virtio requires you to reconfigure your images to interact with the new drivers. For example, you will need to rename the root file system of the guest machine to /dev/vda1, instead of the current EC2 and Eucalyptus default device name /dev/sda1. Please note that reconfiguring images for use with virtio makes them unsuitable for direct transfer between a virtio environment (such as Eucalyptus configured for virtio) and a non-virtio environment (such as EC2).