Stop using stderr so the output is more readable on buildbot.
Otherwise stderr arrives before stdout in apply_issue step.

TBR=rogerta@chromium.org
BUG=153284


Review URL: https://chromiumcodereview.appspot.com/11038002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@159508 0039d316-1c4b-4281-b951-d872f2087c98