nix {run,shell}: Print a better error message if the store is not local
nix {run,shell}: Print a better error message if the store is not local

Closes #6317

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