nixos/acme: Allow disabling bash tracing
nixos/acme: Allow disabling bash tracing

This is horrible if you want to debug failures that happened during
system switches but your 30-ish acme clients spam the log with the same
messages over and over again.

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