If we don't have permission to create the metrics.cfg file, print a
notice and disable metrics collection.

Bug: 870231
Change-Id: I784e988ed021daef0fb07c08f1da44718581b1b9
Reviewed-on: https://chromium-review.googlesource.com/1166322Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>