--module needs to be specified with terraform output

[kitsunde]

Otherwise this happens:

$ terraform output terraform_config
The state file either has no outputs defined, or all the defined
outputs are empty. Please define an output in your configuration
with the `output` keyword and run `terraform refresh` for it to
become available. If you are using interpolation, please verify
the interpolated value is not empty. You can use the
`terraform console` command to assist.