New version correctly handle LUCI_CONTEXT['local_auth'] environment.

BUG=730878
R=dnj@chromium.org, smut@google.com

Change-Id: I1ed9c48eb15010856502d35baf140c97d1dd566c
Reviewed-on: https://chromium-review.googlesource.com/559954Reviewed-by: Daniel Jacques <dnj@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>