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: If17dd627708f03824939ba062b498675253b11d7
677ab44170