If nix_system_path points to a file in a directory that doesn't exist, apply fails

[ocharles]

You end up with something like nix_nixos.new: open /vagrant/mono/ops/derived/nixos/new/configuration.nix: no such file or directory. If you create nix_nixos.new: open /vagrant/mono/ops/derived/nixos/new then everything is fine. I think this plugin should create the directory of the file in question.

[andrewchambers]

Thanks for reporting, can't say when I will have time to look at this, hopefully not too long.