benchmarks/stress-ng: updating to 0.8.14
Changes: http://kernel.ubuntu.com/git/cking/stress-ng.git/commit/?h=V0.08.14&id=64e90341ba9262c4fe2dcbded3d3a524d70ff415
Approved by: olivier (mentor) Differential Revision: https://reviews.freebsd.org/D12335