block: Remove qcow compat alias

Update external consumers to use formats::qcow::internal instead
of the top level qcow alias. Keep a crate private use for the
QcowError variant in lib.rs.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

vhost_user_block/src/lib.rs

@@ -19,7 +19,7 @@ use std::sync::{Arc, Mutex, RwLock, RwLockWriteGuard};
 use std::time::Instant;
 use std::{convert, io, process, result};
 
-use block::qcow::RawFile;
+use block::formats::qcow::internal::RawFile;
 use block::{Request, RequestType, VirtioBlockConfig, build_serial};
 use libc::EFD_NONBLOCK;
 use log::{debug, error, info, warn};