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: I7e3b2835f1cee2525b02960e2b7e4ee238373bcc

defaults/main.yml

@@ -187,6 +187,7 @@ ironic_pip_packages:
   - osprofiler
   - proliantutils
   - PyMySQL
+  - pymemcache
   - pysnmp
   - python-dracclient
   - python-ilorest-library
@@ -202,6 +203,9 @@ ironic_inspector_pip_packages:
   - ironic-inspector
   - python-ironic-inspector-client
 
+# Memcached override
+ironic_memcached_servers: "{{ memcached_servers }}"
+
 ## Oslo Messaging Info
 # RPC
 ironic_oslomsg_rpc_host_group: "{{ oslomsg_rpc_host_group | default('rabbitmq_all') }}"

templates/ironic.conf.j2

@@ -9,7 +9,7 @@ debug = {{ debug }}
 auth_strategy = {{ ironic_auth_strategy }}
 host = {{ inventory_hostname }}
 
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ ironic_memcached_servers }}
 enabled_network_interfaces = {{ ironic_enabled_network_interfaces_list }}
 default_network_interface = {{ ironic_default_network_interface }}
 
@@ -131,7 +131,7 @@ username = {{ ironic_service_user_name }}
 password = {{ ironic_service_password }}
 region_name = {{ keystone_service_region }}
 
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ ironic_memcached_servers }}
 
 token_cache_time = 300