Update /etc/cinder/cinder.conf.sample for memcache

It appears that an update to keystone middleware earlier today
added options for memcache_secret_key, memcache_pool_dead_retry,
memcache_pool_maxsize, memcache_pool_socket_timeout,
memcache_pool_unused_timeout, memcache_pool_conn_get_timeout and
memcache_use_advanced_pool.  The commit that added these options
was: a7beb50b38be5c3dd4c44d68ad79d1bb206dab6b - "Add an optional
advanced pool of memcached clients".

This has once again caused the check_uptodate.sh script to fail.

This patch updates cinder.sample.conf .

Change-Id: Ibcf19ccc81a56a9a3e795022e3e07bc061fa9401
Closes-bug: 1374154