When trying to build a VM using `nixos-build-vms` with a configuration
that doesn't evaluate, an error "at `<unknown-file>`" is usually shown.
This happens since the `build-vms.nix` creates a VM-network of
NixOS-configurations that are attr-sets or functions and don't contain
any file information. This patch manually adds the `_file`-attribute to
tell the module-system which file contained broken configuration:
```
$ cat vm.nix
{ vm.invalid-option = 1; }
$ nixos-build-vms vm.nix
error: The option `invalid-option' defined in `/home/ma27/Projects/nixpkgs/vm.nix@node-vm' does not exist.
(use '--show-trace' to show detailed location information)
```
In 0945178b3c6fd9e33002dd6e3c6f77dfca49565a we decided that Perl-based
VM tests should be deprecated and will be removed between 20.03 and
20.09. So let's switch `nixos-build-vms(8)` to python as well (which is
entirely interactive, so other scripts won't break).
In my experience, the test-driver isn't used most of the time, so this
patch is mainly supposed to get rid of the (probably misleading)
deprecation warning when running `nixos-build-vms`. Apart from that, the
interface for python's test-driver is way nicer.
Also simplified the argument parsing to write all currently supported
CLI options into a bash array and pass this to `nix-build`.
Also documented `--option` usage in the corresponding manpage.
Previously I got the following error message:
```
error: opening file '/home/ma27/Projects/nixpkgs/nixos/modules/installer/default.nix': No such file or directory
```
Probably related to 6c68fbd4e1f8beac39cb1f499ff90c78256262d6.
This reverts commit 10addad6035034b2b78f3c74ef436cd7146d5231, reversing
changes made to 7786575c6c0e1b010d46ad00b14d0bb5bf08d7d2.
NixOS scripts should be kept in the NixOS source tree, not in
pkgs. Moving them around is just confusing and creates unnecessary
code/history churn.
Move all the nixos-* scripts from the nixos distribution as real
packages in the pkgs/ package set.
This allows non-nixos users to run the script as well. For example,
deploying a remote machine with:
nixos-rebuild --target-host root@hostname --build-host root@hostname
