ZTS: Make use of optimal CPU pinning

With CPU pinning, we should get some speedup because of better
cpu cache re-use.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes #16641