Add 'nix-name and 'system properties to hydra objects. This way Cuirass won't
have to go through every derivation to add those properties.
* gnu/ci.scm (package->alist, image-jobs, system-test-jobs, tarball-jobs): Add
'nix-name and 'system properties.
* build-aux/hydra/guix-modular.scm (build-job): Ditto.