block_util: Add new traits for handling disk files asynchronously

Both DiskFile and AsyncIo traits are introduced to allow all kind of
files (RAW, QCOW, VHD) to be able to handle asynchronous access to the
underlying file.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

block_util/src/lib.rs

@@ -13,6 +13,8 @@ extern crate log;
 #[macro_use]
 extern crate serde_derive;
 
+pub mod async_io;
+
 #[cfg(feature = "io_uring")]
 use io_uring::Probe;
 use io_uring::{opcode, squeue, IoUring};