Refactor memcached_servers

This patch aims to add a prefix for memcached_server
on each role to give the ability for deployers to
override the location of memcached cluster. I.e users
wants to create a single memcached cluster with k8s
for each service.

We also add pymemcache based on [1] and fix zun-docker
systemd config.

[1] https://review.opendev.org/711429

Change-Id: Ic7b31506177ebb0f4f24eaff4db134aace5c0b1a

defaults/main.yml

@@ -263,6 +263,7 @@ zun_pip_packages:
   - oslo_rootwrap
   - osprofiler
   - python-memcached
+  - pymemcache
   - python-zunclient
   - pymysql
   - systemd-python
@@ -272,6 +273,8 @@ zun_pip_packages:
 # TODO(ansmith): Change structure when more backends will be supported
 zun_oslomsg_amqp1_enabled: "{{ zun_oslomsg_rpc_transport == 'amqp' }}"
 
+zun_memcached_servers: "{{ memcached_servers }}"
+
 zun_optional_oslomsg_amqp1_pip_packages:
   - oslo.messaging[amqp1]
 

templates/systemd-docker-override.conf.j2

@@ -1,3 +1,3 @@
 [Service]
 ExecStart=
-ExecStart=/usr/bin/dockerd --group {{ zun_system_group_name }} -H tcp://localhost:2375 -H unix:///var/run/docker.sock --cluster-store etcd://{% for item in groups['zun_api'] %}{{ hostvars[item]['ansible_host'] }}:2379{% if not loop.last %},{% endif %}{% endfor %}
+ExecStart=/usr/bin/dockerd --group {{ zun_system_group_name }} -H tcp://127.0.0.1:2375 -H unix:///var/run/docker.sock --cluster-store etcd://{% for item in groups['zun_api'] %}{{ hostvars[item]['ansible_host'] }}:2379{% if not loop.last %},{% endif %}{% endfor %}

templates/zun.conf.j2

@@ -1071,7 +1071,7 @@ region_name = {{ keystone_service_region }}
 # undefined, tokens will instead be cached in-process. (list value)
 # Deprecated group/name - [keystone_authtoken]/memcache_servers
 #memcached_servers = <None>
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ zun_memcached_servers }}
 
 # In order to prevent excessive effort spent validating tokens, the middleware
 # caches previously-seen tokens for a configurable duration (in seconds). Set