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: I19b74c3bc5119953256d3d8f2a98cb5f23787755
0b9bcc3e5a