Command for accessing terraform outputs

[eschwartz]

The DCE terraform module exposes a number of outputs, which are in some cases necessary for basic usage of the system. For example, the url of the API gateway is accessible from terraform output api_url. Another example is the SNS topic ARNs for lifecycle events (eg. lease-created, etc).

It would be nice if the DCE CLI provided a way to access these values.
Maybe something like:

dce system get <output name>