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/adduser/defaults/main.yml

@@ -1,24 +1,40 @@
 ---
 addusers:
   etcd:
-    name: etcd
+    name: "{{ etcd_user }}"
     comment: "Etcd user"
-    createhome: yes
+    createhome: >-
+      {% if ansible_os_family in ["CoreOS", "Container Linux by CoreOS"] %}no{% else %}yes{% endif %}
     home: "/var/lib/etcd"
     system: yes
-    shell: /bin/nologin
+    shell: /usr/sbin/nologin
+    group: "{{ etcd_group }}"
+    groups: "{{ etcd_cert_group }}"
+    type: >-
+      {% if ansible_os_family in ["CoreOS", "Container Linux by CoreOS"] %}cloud-init{% endif %}
   kube:
-    name: kube
+    name: "{{ kubelet_user }}"
     comment: "Kubernetes user"
-    shell: /sbin/nologin
+    shell: /usr/sbin/nologin
     system: yes
-    group: "{{ kube_cert_group }}"
+    group: "{{ kubelet_group }}"
+    groups: "{{ etcd_cert_group }},{{ kube_cert_group }}"
     createhome: no
+  netplug:
+    name: "{{ netplug_user }}"
+    comment: "Network plugin user"
+    createhome: no
+    system: yes
+    shell: /usr/sbin/nologin
+    group: "{{ netplug_group }}"
+    groups: "{{ etcd_cert_group }}"
 
 adduser:
   name: "{{ user.name }}"
   group: "{{ user.name|default(None) }}"
+  groups: "{{ user.groups|default(None) }}"
   comment: "{{ user.comment|default(None) }}"
   shell: "{{ user.shell|default(None) }}"
   system: "{{ user.system|default(None) }}"
   createhome: "{{ user.createhome|default(None) }}"
+  type: "{{ user.type|default(None) }}"