Drop linux capabilities and rework users/groups

* Drop linux capabilities for unprivileged containerized
  worlkoads Kargo configures for deployments.
* Configure required securityContext/user/group/groups for kube
  components' static manifests, etcd, calico-rr and k8s apps,
  like dnsmasq daemonset.
* Rework cloud-init (etcd) users creation for CoreOS.
* Fix nologin paths, adjust defaults for addusers role and ensure
  supplementary groups membership added for users.
* Add netplug user for network plugins (yet unused by privileged
  networking containers though).
* Grant the kube and netplug users read access for etcd certs via
  the etcd certs group.
* Grant group read access to kube certs via the kube cert group.
* Remove priveleged mode for calico-rr and run it under its uid/gid
  and supplementary etcd_cert group.
* Adjust docs.
* Align cpu/memory limits and dropped caps with added rkt support
  for control plane.

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

roles/etcd/tasks/set_facts.yml

@@ -0,0 +1,17 @@
+---
+- name: Etcd | get etcd user ID
+  shell: /usr/bin/id -u {{ etcd_user }} || echo 0
+  register: etcd_uid
+
+- name: Etcd | get etcd group ID
+  shell: /usr/bin/getent group {{ etcd_group }} | cut -d':' -f3 || echo 0
+  register: etcd_gid
+
+- name: Etcd | get etcd cert group ID
+  shell: /usr/bin/getent group {{ etcd_cert_group }} | cut -d':' -f3 || echo 0
+  register: etcd_cert_gid
+
+- set_fact:
+    etcd_user_id: "{{ etcd_uid.stdout }}"
+    etcd_group_id: "{{ etcd_gid.stdout }}"
+    etcd_cert_group_id: "{{ etcd_cert_gid.stdout }}"