Also expand parameters in lists of strings

[hmaarrfk]

Previously if one had a list of strings, expressions such as {{ PREFIX }} or {{ ENV_NAME }} would not get expanded

• Add a test

Description

I wanted to write a command that looks like {{ PREFIX }}/bin/my_app-{{ ENV_NAME }}

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[hmaarrfk]

Pointers on where to add a test would be appreciated if you want one.
also need to add tests for: #334

[marcoesters]

Pointers on where to add a test would be appreciated if you want one. also need to add tests for: #334

tests/test_api.py is probably the best place for those tests.