qemu-img: Use strerror() for generic resize error

Emitting the plain error number is not very helpful. Use strerror()
instead.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20160615153630.2116-2-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>

qemu-img.c

@@ -3283,7 +3283,7 @@ static int img_resize(int argc, char **argv)
         error_report("Image is read-only");
         break;
     default:
-        error_report("Error resizing image (%d)", -ret);
+        error_report("Error resizing image: %s", strerror(-ret));
         break;
     }
 out: