Integrate with terraform-landscape

[pickgr]

Feature request to integrate/include the following project:

https://github.com/coinbase/terraform-landscape

and add an option for outputting terraform plans through the gem.

Note that is already possible to download the landscape gem independently and run commands like

bin/covalence <env>:<stack>:plan | landscape

[blakeneyops]

I believe this should be possible now. You'll need to install the gem in the container at runtime and then either use the arg config parameter in the stack data or pass the extra option on the command line using the -- after the Covalence task.