vm-virtio: Add vhost-user-blk implementation

vhost-user-blk has better performance than virtio-blk, so we need
add vhost-user-blk support with SPDK in Rust-based VMMs.

Signed-off-by: Yang Zhong <yang.zhong@intel.com>

vm-virtio/src/lib.rs

@@ -130,6 +130,8 @@ pub enum ActivateError {
     VhostUserSetup(vhost_user::Error),
     /// Failed to setup vhost-user daemon.
     VhostUserNetSetup(vhost_user::Error),
+    /// Failed to setup vhost-user daemon.
+    VhostUserBlkSetup(vhost_user::Error),
 }
 
 pub type ActivateResult = std::result::Result<(), ActivateError>;