- Use extra-trusted-users to avoid overriding the default set of trusted
users and causing permission issues.
- Add hydra and hydra-www users which also need permissions.
Nixpkgs only contains a `hydra_unstable`, not `hydra`, package, so
adjust the default accordingly, and then override it to our package in
the separate module which does that.
(cherry picked from commit e149da7b9bbc04bd0b1ca03fa0768e958cbcd40e)
Due to newer nixpkgs, there were a number of things that could be
cleaned up in the process.
(cherry picked from commit 743795b2b090a5cdfe8bd90120add8db7770086a)
Janik Haag
Pierre Bourdon
