Adding multi-node DevStack template for Ubuntu

Adding a template that deploys a multi-node OpenStack installation using
DevStack. This template has been tested on Ubuntu and may work as-is on
Debian too.

Note that the security group resources require to use Neutron and Havana
Heat.

Change-Id: Ibdf4fe7407913f75b2253b09639554c013d31c01
Merge "Adding multi-node DevStack template for Ubuntu"