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: I5ce2be9e7a8a648cbb734a2e418d434e7991e298

defaults/main.yml

@@ -62,6 +62,7 @@ masakari_pip_packages:
   - keystonemiddleware
   - osprofiler
   - PyMySQL
+  - pymemcache
   - python-masakariclient
   - python-novaclient
   - python-keystoneclient
@@ -71,6 +72,9 @@ masakari_pip_packages:
   - uwsgi
   - keystoneauth1
 
+# Memcached override
+masakari_memcached_servers: "{{ memcached_servers }}"
+
 masakari_monitor_pip_packages:
   - masakari-monitors
   - systemd-python

templates/masakari.conf.j2

@@ -34,7 +34,7 @@ user_domain_id = {{ masakari_service_project_domain_id }}
 project_name = {{ masakari_service_project_name }}
 username = {{ masakari_service_user_name }}
 password = {{ masakari_service_password }}
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ masakari_memcached_servers }}
 memcache_security_strategy = ENCRYPT
 memcache_secret_key = {{ memcached_encryption_key }}
 service_token_roles_required = True