The option "queue-size" for virtio-blk was added in qemu-2.12.0, and
default value increased from qemu-5.0.0.
However, increasing this value may lead to drop of random access
performance.
Signed-off-by: Hiroki Narukawa <hnarukaw@yahoo-corp.jp>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>