Install Guide: Basic arch diagram showing services on each node

Co-Authored-By: Andreas Jaeger <jaegerandi@gmail.com>

backport: stable/havana

Cherry-Pick: https://review.openstack.org/#/c/51683/
Change-Id: Ief11613a799a8dcfa07a487e0e9c2a16e25a07fd
Merge "Install Guide: Basic arch diagram showing services on each node" into stable/havana