login: Prefer /run over /var/run.

/var lives on the stateful partition, while /run is a tmpfs. Normally,
/var/run is a symlink to /run, but if a device is compromised, the
contents of /var cannot be trusted.

TEST=Can boot/login with changes.

Change-Id: I06aa3491ad4897eecafe835611a0d837b22faef4
Reviewed-on: https://chromium-review.googlesource.com/388145
Commit-Ready: Ricky Zhou <rickyz@chromium.org>
Tested-by: Ricky Zhou <rickyz@chromium.org>
Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
4 files changed