stress-ng fork updated to 91ec6bcc (V0.15.00)

[Po-Hsu Lin]

Hello folks,

I have our stress-ng fork updated to 91ec6bcc (V0.15.00)
Apart from tests covered by Colin, this version has been tested on our
bare-metal pool with kernels in 20221010 and 20221114 cycle.

Here is the note from Colin for this update:
It contains two new stressors, one to exercise the scheduler for race
conditions --race-sched and one to exercise a ring of fifos
(--ring-fifo).

I've added a load of metrics to each stressor (probably only useful
for performance regression testing) and a lot more bug fixes for weird
issues found across a range of POSIX/UNIX systems and hardware. I've
also added a bunch more stressor methods to increase code testing.

Thanks
Sam