misc: block: drop extern crate, use modern rust

This commit is part of a series of similar commits.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

block/src/qcow/mod.rs

@@ -19,6 +19,7 @@ use std::str;
 
 use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
 use libc::{EINVAL, EIO, ENOSPC};
+use log::error;
 use remain::sorted;
 use thiserror::Error;
 use vmm_sys_util::file_traits::{FileSetLen, FileSync};