Rietveld doesn't post the message when it is too large.

R=petermayo@chromium.org
BUG=
TEST=Now the CQ should stop having weird case where it doesn't post a message on
CQ failure. It was because the message was simply too long!


Review URL: http://codereview.chromium.org/10383004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@135326 0039d316-1c4b-4281-b951-d872f2087c98