Increase the number of CDot VMs

With the CDot Redis migration coming to a conclusion, we should start scaling CDot VMs out, see if things are working out as expected.

Action items

• Make sure the Rails app is able to handle two different versions running at once (e.g. able to handle old and new DB schemas when a deploy is underway)
• Make sure Ansible deploy playbook is serialized so we don't deploy to all hosts at once
• Increase stg-ref VMs to 2
• Increase stg VMs to 2
• Increase prd VMs to 2