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/templates/users.j2

@@ -0,0 +1,15 @@
+#cloud-config
+users:
+- name: {{ user.name  }}
+  gecos: {{ user.comment }}
+  system: {{ user.system|bool }}
+  no-log-init: {{ user.system|bool }}
+  primary-group: {{ user.group }}
+  no-create-home: {{ not user.createhome|bool }}
+  homedir: {{ user.home }}
+  shell: {{ user.shell }}
+  groups: |
+    {% for g in user.groups.split(',') %}
+    - {{ g }}
+    {% endfor %}
+    #