Fix Hydra VM tests

Dependencies

• [2] KVDOL4OZ hydra-module: Don't rely on su being available.
• [3] T4DBPQOF hydra-module: Run hydra-init during hydra-init.service
• [4] V4R3SIRM hydra-module.nix: Don't use a password
• [5] TTZ26BJQ Unify Hydra's NixOS module with the one used for hydra.nixos.org
• [6] ASPNI2AO hydra-module.nix: Automatically create postgres db user for hydra and an admin hydra account
• [*] D3MDJONY

Change contents

• edit in hydra-module.nix at line 255
  [3.99]

  [2.0]
  + path = [ pkgs.utillinux ];
• replacement in hydra-module.nix at line 272
  [3.261]→[3.261:334](∅→∅),[3.334]→[3.345:425](∅→∅),[3.345]→[3.345:425](∅→∅)
  − ${config.services.postgresql.package}/bin/createuser hydra

  − ${config.services.postgresql.package}/bin/createdb -O hydra hydra
  [3.261]

  [3.335]
  + runuser -u ${config.services.postgresql.superUser} -- ${config.services.postgresql.package}/bin/createuser hydra

  + runuser -u ${config.services.postgresql.superUser} -- ${config.services.postgresql.package}/bin/createdb -O hydra hydra