run-make-check.sh: build ctest cpu resource pool from sched_getaffinity

gen_ctest_resource_file assumed online CPUs are a contiguous 0..nproc-1 range.
When a middle core is hot-offlined (e.g. for a hardware fault), that both hands
out the offline cpu id and drops an online one; crimson seastar unittests feed
the ctest resource id straight to seastar --cpuset, so hitting the offline id
aborts with "Bad value for --cpuset: N not allowed".

Use the CPUs actually schedulable by the process via sched_getaffinity().

Signed-off-by: Sun Yuechi <sunyuechi@iscas.ac.cn>