give virtual base a defaults file, resnap demands it for now.
initial work on #32, to support flat disk images (no partitions)
small tweaks/cleanups, only funcitonal difference is setting root devicename to sda1 for device mappings for pvm/ebs (seems right, may have to unwind)
get the rootfs label right, dont "fix" grub on flat images
attempt to use extlinux to get though the hvm boot issue on flat image
achievement: ultimate bootfix? first hvm, no partition boot, via extlinux (was missing a step). block device mappings may need adjustment, root mounts as /dev/xvda, where we expect /dev/xvda1