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/network_plugin/calico/tasks/main.yml

@@ -9,15 +9,16 @@
   template:
     src: "cni-calico.conf.j2"
     dest: "/etc/cni/net.d/10-calico.conf"
-    owner: kube
+    owner: "{{ kubelet_user }}"
+    group: "{{ kubelet_group }}"
 
 - name: Calico | Create calico certs directory
   file:
     dest: "{{ calico_cert_dir }}"
     state: directory
     mode: 0750
-    owner: root
-    group: root
+    owner: "{{ netplug_user }}"
+    group: "{{ netplug_group }}"
 
 - name: Calico | Link etcd certificates for calico-node
   file: