Run RISC-V VMs from remote compressed images

nbdkit --filter=cow --filter=xz curl \
    https://dl.fedoraproject.org/pub/alt/risc-v/
    disk-images/fedora/rawhide/20190703.n.0/
    Developer/Fedora-Developer-Rawhide-20190703.n.0-sda.raw.xz

qemu-system-riscv64 \
    -nographic \
    -machine virt \
    -smp 8 \
    -m 2G \
    -drive file.driver=nbd,file.host=localhost,
           file.port=10809