[9.20] chg: usr: Follow the number of CPU set by taskset/cpuset
Administrators may wish to constrain the set of cores that BIND 9 runs on via the 'taskset', 'cpuset' or 'numactl' programs (or equivalent on other O/S).
If the admin has used taskset, the named
will now follow to automatically use the given number of CPUs rather than the system wide count.
Closes #4884 (closed)
Backport of MR !9398 (merged)