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/vars/debian.yml

@@ -1,15 +0,0 @@
----
-addusers:
-  - name: etcd
-    comment: "Etcd user"
-    createhome: yes
-    home: "/var/lib/etcd"
-    system: yes
-    shell: /bin/nologin
-
-  - name: kube
-    comment: "Kubernetes user"
-    shell: /sbin/nologin
-    system: yes
-    group: "{{ kube_cert_group }}"
-    createhome: no