Reserve core for tests

[osogi]

It turns out I never added it before.
It should be implemented it as carefully as possible, because if something goes wrong, it can disable the whole core for the user.

Links with some info:
https://man7.org/linux/man-pages/man7/cpuset.7.html
https://stackoverflow.com/questions/72124705/within-rt-linux-is-it-possible-to-enforce-linux-background-tasks-to-run-on-a-sp
https://documentation.suse.com/sle-rt/12-SP5/html/SLE-RT-all/cha-shielding-cpuset.html