Don't work with cgroups v2

[mireq]

Uwsgi uses old taks file which is not supported on new systems with cgroups v2:

using Linux cgroup /sys/fs/cgroup/uwsgi/project with mode 777 open("/sys/fs/cgroup/uwsgi/project/tasks"): Permission denied [core/utils.c line 234]

[rcarmo]

I'd love to see this fixed too. This makes uwsgi unusable in modern systems.