file_lock: Add fallback directory

This adds a fallback directory in case SYSTEM_LOCKFILE_DIR is
unavailable. Since this is a band-aid meant to help older systems
auto-update, the fallback path is hardcoded to "/tmp" as to avoid
polluting the overall lockfile API.

BUG=chromium:616620
BRANCH=none
TEST=Tested on veyron_jaq by removing /run/lock and seeing
mosys, flashrom, and ectool run successfully with
firmware_utility_lock in /tmp.

Change-Id: Icba3381bfdc23673346d895b87b25afe3bfb8450
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/348840
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
(cherry picked from commit 2c7fbec0d1319d9426fbdce88105c72b1234c49a)
Reviewed-on: https://chromium-review.googlesource.com/350125
1 file changed