Deploy as part of CI

[grahamc]

At the end of the day, nixops deploy is the key feature we have here. We should do it as part of CI. Also nice would be being able to do deploys with various backends, like nixops-aws to see if PRs to nixops breaks a plugin.

[roberth]

As a low hanging fruit, we could test the none backend in a nixosTest, because it does not depend on real cloud services. As such, it will be easy to run, which is actually kinda great.

[roberth]

This seems like a good starting point: NixOS/nixpkgs#142035