faft: Better descriptions of test failures

BUG=None
TEST=None, trivial change.

Change-Id: Ic629856f1c9821bcfd5998e69de13c96f78c8bc1
Reviewed-on: https://gerrit.chromium.org/gerrit/37499
Commit-Ready: Tom Wai-Hong Tam <waihong@chromium.org>
Reviewed-by: Tom Wai-Hong Tam <waihong@chromium.org>
Tested-by: Tom Wai-Hong Tam <waihong@chromium.org>
1 file changed