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: I571a0ac9417767af413937e871ea6cdf156f2d75

defaults/main.yml

@@ -197,11 +197,15 @@ trove_pip_packages:
   - osprofiler
   - pexpect
   - PyMySQL
+  - pymemcache
   - python-troveclient
   - python-memcached
   - systemd-python
   - trove
 
+# Memcached override
+trove_memcached_servers: "{{ memcached_servers }}"
+
 trove_optional_oslomsg_amqp1_pip_packages:
   - oslo.messaging[amqp1]
 

templates/trove.conf.j2

@@ -92,7 +92,7 @@ username = {{ trove_service_user_name }}
 password = {{ trove_service_password }}
 region_name = {{ keystone_service_region }}
 
-memcached_servers = {{ memcached_servers }}
+memcached_servers = {{ trove_memcached_servers }}
 token_cache_time = 300
 
 # if your memcached server is shared, use these settings to avoid cache poisoning