lib: test for_each_numa_cpus()

lib: test for_each_numa_cpus()

Test for_each_numa_cpus() output to ensure that:
 - all CPUs are picked from NUMA nodes with non-decreasing distances to the
   original node;
 - only online CPUs are enumerated;
 - the macro enumerates each online CPUs only once;
 - enumeration order is consistent with cpumask_local_spread().

The latter is an implementation-defined behavior. If cpumask_local_spread()
or for_each_numa_cpu() will get changed in future, the subtest may need
to be adjusted or even removed, as appropriate.

It's useful now because some architectures don't implement numa_distance(),
and generic implementation only distinguishes local and remote nodes, which
doesn't allow to test the for_each_numa_cpu() properly.

Suggested-by: Valentin Schneider <vschneid@redhat.com> (for node_distance() test)
Signed-off-by: Yury Norov <yury.norov@gmail.com>