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: Iefac95507d189b86371026e17465adf15b1bf410

defaults/main.yml

@@ -154,11 +154,15 @@ gnocchi_pip_packages:
   - gnocchiclient
   - "gnocchi[keystone,mysql,{{ gnocchi_storage_driver == 'ceph' | ternary('ceph_alternative', gnocchi_storage_driver) }}]"
   - osprofiler
+  - pymemcache
   - python-memcached
   - kazoo
   - redis
   - systemd-python
 
+# Memcached override
+gnocchi_memcached_servers: "{{ memcached_servers }}"
+
 # This variable is used by the repo_build process to determine
 # which host group to check for members of before building the
 # pip packages required by this role. The value is picked up

templates/gnocchi.conf.j2

@@ -33,7 +33,7 @@ project_name = {{ gnocchi_service_project_name }}
 username = {{ gnocchi_service_user_name }}
 password = {{ gnocchi_service_password }}
 
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ gnocchi_memcached_servers }}
 token_cache_time = 300
 
 # if your memcached server is shared, use these settings to avoid cache poisoning