nvme-cli spdk plugin

[Brzezinka, Sebastian]

> Can spdk emulate the way nvme devices expose themselves but in different path prefix?

SPDK right now cannot update sysfs, only CUSE in /dev/spdk/ is available.
https://spdk.io/doc/nvme.html

>NVMe namespaces are created as character devices and their use may be limited for tools expecting block devices.
>Sysfs is not updated by SPDK.
>SPDK NVMe CUSE creates nodes in "/dev/spdk/" directory to explicitly differentiate from other devices. Tools that only search in the "/dev" directory might not work with SPDK NVMe CUSE.