Eliminate the dependency on kernel pseudo-files when running unit tests

This change means that the unit tests no longer need /proc/uptime
or /sys/block/sda/stat in order to operate properly.

As an added bonus, this change enables testing that the output of
bootstat_log() exactly matches the expected content.

BUG=chromium-os:8311
TEST=Run the unit tests

Review URL: http://codereview.chromium.org/5500001

Change-Id: I8a6382ebb9eb3c78c3109f9e12f5b87dfe334a00
4 files changed