cros_image_to_target: use newstyle updates, followup after switching --nooldstyle to be the default

BUG=n0ne
TEST=run the script and see the update go

Change-Id: Ie767edf85876b7864f6425efed1ac554026ecdff

Review URL: http://codereview.chromium.org/6596062

bin/cros_image_to_target.py

@@ -450,6 +450,7 @@ class PingUpdateResponse(StringUpdateResponse):
       codebase="%s"
       hash="%s"
       sha256="%s"
+      IsDelta="true"
       needsadmin="false"
       size="%s"
       status="ok"/>