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]

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

Change-Id: I1f808534cb115224c17eb82791b2178172547216

defaults/main.yml

@@ -332,6 +332,11 @@ neutron_plugin_base:
   - router
   - metering
 
+###
+### Memcache override
+###
+neutron_memcached_servers: "{{ memcached_servers }}"
+
 ###
 ### ML2 Plugin Configuration
 ###

templates/neutron.conf.j2

@@ -181,7 +181,7 @@ username = {{ neutron_service_user_name }}
 password = {{ neutron_service_password }}
 region_name = {{ keystone_service_region }}
 
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ neutron_memcached_servers }}
 
 token_cache_time = 300
 

vars/main.yml

@@ -33,6 +33,7 @@ neutron_pip_packages:
   - neutron
   - osprofiler
   - PyMySQL
+  - pymemcache
   - python-memcached
   - systemd-python