[autotest] Use rsync instead of cp in gs_offloader.

gsutil cp uses a lot of connections and has a big cpu overhead. Using
rsync instead allows
a) incremental uploads: If an upload failed, it doesn't need to be
   re-started from scratch
b) faster uploads, because many files are sent over the same
   connection.

BUG=None
DEPLOY=gs_offloader
TEST=Ran suites and tested with local results dir and testing bucket.

Change-Id: I6e920dfccba5b4d2b0b1a19031f1922a0758a3cc
Reviewed-on: https://chromium-review.googlesource.com/220147
Tested-by: Jakob Jülich <jakobjuelich@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Commit-Queue: Jakob Jülich <jakobjuelich@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index 16f2d4a..c360eb0 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -198,6 +198,7 @@
 crash_server: http://172.17.40.24:8082
 sharding_factor: 1
 infrastructure_user: chromeos-test
+gs_offloader_use_rsync: False
 
 firmware_url_pattern: %s/static/%s/firmware_from_source.tar.bz2
 factory_image_url_pattern: %s/static/canary-channel/%s/factory_test/chromiumos_factory_image.bin