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: Ie50f529975e8f2ae1bf66136240b3901f08b51a4

defaults/main.yml

@@ -25,6 +25,8 @@ nova_ceilometer_enabled: False
 # Enable/Disable nova versioned notification
 nova_versioned_notification_enabled: False
 
+nova_memcached_servers: "{{ memcached_servers }}"
+
 ## Verbosity Options
 debug: False
 
@@ -465,6 +467,7 @@ nova_pip_packages:
   - nova
   - osprofiler
   - PyMySQL
+  - pymemcache
   - python-memcached
   - systemd-python
 

templates/nova.conf.j2

@@ -64,7 +64,7 @@ transport_url = {{ nova_oslomsg_notify_transport }}://{% for host in nova_osloms
 [cache]
 enabled = true
 backend = oslo_cache.memcache_pool
-memcache_servers = {{ memcached_servers }}
+memcache_servers = {{ nova_memcached_servers }}
 
 
 # Cinder