ProgressBar: Respect verbosity level
ProgressBar: Respect verbosity level

This makes its behaviour consistent with SimpleLogger.

NixOS/nix,rycee/nix,rycee/nix,rycee/nix,NixOS/nix,NixOS/nix,rycee/nix,rycee/nix,NixOS/nix,NixOS/nix