Use hiera interpolation for memcached_network
Use hiera interpolation for memcached_network

After [1] iptables rules are not set for memcached service
thus services relying on memcached were not functioning well.
With [2] it's requrired to use hiera interpolation for service
configs, this patch fixes it for memcached_network.

[1] https://review.openstack.org/#/c/551292
[2] https://review.openstack.org/#/c/526692

Related-Bug: #1757556
Closes-Bug: #1763009
Change-Id: If9b274192ea4738f455a6106ff1a62eb4e7a5c91

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates