support nvme volume by spdk vhost and rdma

OpenStack currently supports the NVME disk approach, through the NVME CLI to mount the NVME disk into the QEMU virtual machine, QEMU virtual machine and disk I/O process still need to go through the Linux kernel, which will not be able to fully exploit the full power of RDMA.

The SPDK driver provides the vhost app, which can improve QEMU virtual machine I/O performance by bypassing the Linux kernel

And SPDK vhost supports local disk, if you want to attach remote NVMe disk, you can use the combination of SPDK vhost + RDMA, which makes use of the ability of vhost, but also through RDMA data directly transferred to the application layer, bypassing the kernel.