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-host.service.j2

@@ -0,0 +1,19 @@
+[Unit]
+Description=etcd-proxy
+After=network.target
+
+[Service]
+Type=notify
+User=etcd
+PermissionsStartOnly=true
+EnvironmentFile=/etc/etcd-proxy.env
+ExecStart={{ bin_dir }}/etcd
+ExecStartPre=/bin/mkdir -p /var/lib/etcd-proxy
+ExecStartPre=/bin/chown -R etcd: /var/lib/etcd-proxy
+NotifyAccess=all
+Restart=always
+RestartSec=10s
+LimitNOFILE=40000
+
+[Install]
+WantedBy=multi-user.target