block: Add DiskFileError::Clone variant

Add a Clone variant to DiskFileError for error handling in
the upcoming AsyncDiskFile::try_clone() implementations.

This variant will be used by RawFileDisk and RawFileDiskSync
when cloning the underlying file descriptor fails.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

block/src/async_io.rs

@@ -24,6 +24,8 @@ pub enum DiskFileError {
     /// Resize failed
     #[error("Resize failed")]
     ResizeError(#[source] std::io::Error),
+    #[error("Failed cloning disk file")]
+    Clone(#[source] std::io::Error),
 }
 
 pub type DiskFileResult<T> = std::result::Result<T, DiskFileError>;