Revert "Drop linux capabilities and rework users/groups"

docs/security.md

inventory/group_vars/all.yml

roles/adduser/defaults/main.yml

roles/adduser/handlers/main.yml

roles/adduser/tasks/main.yml

roles/adduser/templates/users.j2

roles/adduser/vars/coreos.yml

roles/adduser/vars/debian.yml

roles/adduser/vars/redhat.yml

roles/dnsmasq/defaults/main.yml

roles/dnsmasq/templates/dnsmasq-ds.yml

roles/etcd/defaults/main.yml

roles/etcd/files/make-ssl-etcd.sh

roles/etcd/meta/main.yml

roles/etcd/tasks/gen_certs.yml

roles/etcd/tasks/main.yml

roles/etcd/tasks/pre_upgrade.yml

roles/etcd/tasks/set_facts.yml

roles/etcd/templates/etcd-docker.service.j2

roles/etcd/templates/etcd-rkt.service.j2