In environments where memcached_listen is overridden to listen on multiple
IP addresses, the memcached-flush upgrade playbook will fail because it is
trying to flush an IP like "172.29.236.219,127.0.0.1"
This will fix the memcached flush playbook to flush only the first listen IP
that is specified in the memcached.conf file.
Change-Id: I7b34933c1569b97f3cd23bb3db86dd0067fc846e