Only print out files that change when rsyncing.

Change-Id: Ic139743a308fdba4c5d650aa7229abc17f7e58e1
diff --git a/aos/prime/downloader/downloader.py b/aos/prime/downloader/downloader.py
index 6c8cb4b..26ef19a 100644
--- a/aos/prime/downloader/downloader.py
+++ b/aos/prime/downloader/downloader.py
@@ -34,7 +34,7 @@
   ssh_target = '%s@%s' % (user, hostname)
 
   subprocess.check_call(
-      ['rsync', '-v', '-z', '--copy-links'] + srcs +
+      ['rsync', '-c', '-v', '-z', '--copy-links'] + srcs +
       ['%s:%s' % (ssh_target, target_dir)])
   subprocess.check_call(
       ('ssh', ssh_target, '&&'.join([