Allow blockdevs to match the feature already present in qemu-nbd -D.
Enhance iotest 223 to cover it.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMaxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20191114024635.11363-5-eblake@redhat.com>