Update ansible variable templates to allow for envsubst
Created by: slifty
The various ansible variable templates use the format ___VARIABLE_NAME___ to indicate placeholder values that need to be populated. This makes sense, BUT, if we swap that to ${VARIABLE_NAME} it allows us to use the envsubst utility to more easily generate populated templates.
This will make it easier for us to script the creation of new machines (for the purposes of virtual machine based development environment at first, but eventually maybe for containers too). Since it's just the template file and these values get replaced this shouldn't have any impact on functionality.
