Use Terraform Data for Ansible Inventory

• Changes base container to use ruby:2.6-alpine3.10
• Adds new script generate_ansible_config.rb
• Adds rspec test coverage for generate_ansible_config.rb
• Removes dependency on gce.py for Ansible job inventory
• Generates extra-vars.json using Terraform outputs
• Generates tf_nodes Ansible inventory file
• Extracts Environment-to-ExtraVars JSON mapping logic to configuration file
• Changes .gitlab-ci.yml to use new inventory generation script

Related: team-tasks#438 (closed)

Resolves: gitlab-org/omnibus-gitlab#4568 (moved)

Signed-off-by: Robert Marshall rmarshall@gitlab.com