Add etcd proxy support

* Enforce a etcd-proxy role to a k8s-cluster group members. This
provides an HA layout for all of the k8s cluster internal clients.
* Proxies to be run on each node in the group as a separate etcd
instances with a readwrite proxy mode and listen the given endpoint,
which is either the access_ip:2379 or the localhost:2379.
* A notion for the 'kube_etcd_multiaccess' is: ignore endpoints and
loadbalancers and use the etcd members IPs as a comma-separated
list. Otherwise, clients shall use the local endpoint provided by a
etcd-proxy instances on each etcd node. A Netwroking plugins always
use that access mode.
* Fix apiserver's etcd servers args to use the etcd_access_endpoint.
* Fix networking plugins flannel/calico to use the etcd_endpoint.
* Fix name env var for non masters to be set as well.
* Fix etcd_client_url was not used anywhere and other etcd_* facts
evaluation was duplicated in a few places.
* Define proxy modes only in the env file, if not a master. Del
an automatic proxy mode decisions for etcd nodes in init/unit scripts.
* Use Wants= instead of Requires= as "This is the recommended way to
hook start-up of one unit to the start-up of another unit"
* Make apiserver/calico Wants= etcd-proxy to keep it always up

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
Co-authored-by: Matthew Mosesohn <mmosesohn@mirantis.com>

roles/etcd/templates/etcd-proxy-docker.service.j2

@@ -0,0 +1,28 @@
+[Unit]
+Description=etcd-proxy docker wrapper
+Wants=docker.service
+After=docker.service
+
+[Service]
+User=root
+PermissionsStartOnly=true
+ExecStart={{ docker_bin_dir | default("/usr/bin") }}/docker run --restart=always \
+--env-file=/etc/etcd-proxy.env \
+{# TODO(mattymo): Allow docker IP binding and disable in envfile
+   -p 2380:2380 -p 2379:2379 #}
+--net=host \
+--stop-signal=SIGKILL \
+-v /usr/share/ca-certificates/:/etc/ssl/certs:ro \
+--name={{ etcd_proxy_member_name | default("etcd-proxy") }} \
+{{ etcd_image_repo }}:{{ etcd_image_tag }} \
+{% if etcd_after_v3 %}
+{{ etcd_container_bin_dir }}etcd
+{% endif %}
+ExecStartPre=-{{ docker_bin_dir | default("/usr/bin") }}/docker rm -f {{ etcd_proxy_member_name | default("etcd-proxy") }}
+ExecReload={{ docker_bin_dir | default("/usr/bin") }}/docker restart {{ etcd_proxy_member_name | default("etcd-proxy") }}
+ExecStop={{ docker_bin_dir | default("/usr/bin") }}/docker stop {{ etcd_proxy_member_name | default("etcd-proxy") }}
+Restart=always
+RestartSec=10s
+
+[Install]
+WantedBy=multi-user.target