RFE: Allow user to easily change instance type

[fftux]

Simplify the process for changing the instance type for control nodes.

Permalink to Chat conversation: https://chat.google.com/room/AAAA9bAjK5c/d6agM9GUdhg

[usrbinkat]

need to apply this stubbed variable set across the iac via templates/openshift-install and templates/terraform/global.tfvars.j2 files
https://github.com/CodeSparta/sparta/search?q=m5.xlarge