Make update_scripts failure not mark the build as failed.
Make update_scripts failure not mark the build as failed.

It's annoying especially on Rietveld try job status boxes. Use
warnOnFailure=True, so a FAILURE of this build step will mark the overall build
as having WARNINGS. The remaining steps will still be executed.

R=iannucci@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/16965012

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@207250 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build