metrics daemon: change location of flag files

For security reasons, we changed the location of some flag
files to /var/run from /tmp, but we didn't update this
program to look for the files in their new location.
This corrects the problem.

BUG=chromium:200181
TEST=manually verified that kernel crash counters increase
BRANCH=none

Change-Id: I03efe6179a1ad8dfd4c8cbb1eccf24c7a8494058
Reviewed-on: https://chromium-review.googlesource.com/186692


Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Queue: Luigi Semenzato <semenzato@chromium.org>
Tested-by: Luigi Semenzato <semenzato@chromium.org>