Convert qemu target parent

[afbjorklund]

Currently the kvm target inherits from the same "live cd" parent as boot2docker: qemu_x86_64 Then it copies all the files from the rootfs to a tmpfs, due to the requirements from pivot_root.

It should instead use the "installed" parent, pc_x86_64_bios and a regular filesystem (not initrd) This will make the image larger on disk (since it is no longer compressed) but faster to work with.

The raspberry image currently uses it.

Possibly consider adding a boot partition ?

[afbjorklund]

  partition boot {
    in-partition-table = "no"
    image = "boot.img"
    offset = 0
    size = 512
  }

  partition grub {
    in-partition-table = "no"
    image = "grub.img"
    offset = 512
  }

  partition root {
    partition-type = 0x83
    image = "rootfs.ext2"
  }