Modify qemu_opt_rename to realize renaming all items in opts

Add realization of rename all items in opts for qemu_opt_rename.
e.g:
When add bps twice in command line, need to rename all bps to
throttling.bps-total.

This patch solved following bug:
Bug 1145586 - qemu-kvm will give strange hint when add bps twice for a drive
ref:https://bugzilla.redhat.com/show_bug.cgi?id=1145586

[Resolved conflict with commit 5abbf0ee4d
("block: Catch simultaneous usage of options and their aliases").  Check
for simultaneous use first, and then loop over all options.
--Stefan]

Signed-off-by: Jun Li <junmuzi@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1411537527-16715-1-git-send-email-junmuzi@gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

blockdev.c

@@ -548,6 +548,10 @@ static void qemu_opt_rename(QemuOpts *opts, const char *from, const char *to,
                        "same time", to, from);
             return;
         }
+    }
+
+    /* rename all items in opts */
+    while ((value = qemu_opt_get(opts, from))) {
         qemu_opt_set(opts, to, value);
         qemu_opt_unset(opts, from);
     }