Conform to Terraform best practices

[tpdownes]

1. Configure both google and google-beta providers
2. Ensure that google and google-beta providers have version constraints.
3. Ensure that terraform client has minimum version enforced (choose
   value presently selected by Cloud Foundation Toolkit)
4. Configure each provider with a default zone; the README for generating YAML
   describes zone as an input variable for all modules.
5. Conform to Terraform standard module structure by creating empty
   outputs.tf file
6. Use best practice # instead of // for single-line comment
7. Conform to snake_case Terraform naming convention

[heyealex]

Looks good, just had a couple minor questions/comments.

[heyealex]

Thanks for the info and clarifications!