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.

BUG=chromium:649039
TEST=Can boot/login with changes.

Change-Id: I06aa3491ad4897eecafe835611a0d837b22faef4
Reviewed-on: https://chromium-review.googlesource.com/388145
Commit-Ready: Ricky Zhou <[email protected]>
Tested-by: Ricky Zhou <[email protected]>
Reviewed-by: Mattias Nissler <[email protected]>
Reviewed-by: Dylan Reid <[email protected]>
4 files changed