hw/block/nvme: Generate namespace UUIDs

hw/block/nvme: Generate namespace UUIDs

In NVMe 1.4, a namespace must report an ID descriptor of UUID type
if it doesn't support EUI64 or NGUID. Add a new namespace property,
"uuid", that provides the user the option to either specify the UUID
explicitly or have a UUID generated automatically every time a
namespace is initialized.

Suggested-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Niklas Cassel <Niklas.Cassel@wdc.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>