Add support for registration codes. BUG=chrome-os-partner:11912 TEST=registration_codes_unittest.py, manual end-to-end test Change-Id: Ib5729a44952439e90a0d79e1d87484e5593a9ed3 Reviewed-on: https://gerrit.chromium.org/gerrit/28683 Tested-by: Jon Salz <jsalz@chromium.org> Reviewed-by: Hung-Te Lin <hungte@chromium.org> Commit-Ready: Jon Salz <jsalz@chromium.org>