tests/prometheus-exporters: allow overriding test-node-name
tests/prometheus-exporters: allow overriding test-node-name

allows the prometheus-exporters test abstraction to work with e.g. hyphenated exporter-names

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs