Add the blockstats data and fix the expected output.
Test data was created as:
qemu-img create -f qcow2 img0 10M
qemu-img create -f qcow2 -o "backing_fmt=qcow2,backing_file=img0" img1
qemu-img create -f qcow2 -o "backing_fmt=qcow2,backing_file=img1" img2
...
Reviewed-by: Eric Blake <eblake@redhat.com>
