Create Ansible playbook to roll out configuration

Right now, our Terraform scripts only handle creation of machines in GCP, but not their respective configuration. As it's a task we're doing rather frequently which takes some time, this commit creates an Ansible playbook which automates this task.

On creation of the cluster, our scripts now automatically generate a hosts.ini file containing all necessary connection information. With this file, the admin may now run ./configure-demo-cluster, which will invoke Ansible and automatically generate and apply configuration for each of the nodes, restarting services as required. The task can be run repeatedly in order to update configuration on the target nodes.