nixops: Fix build by disabling the libvirt backend

[adisbladis]

Motivation for this change

NixOps currently does not build because of a dependency that's marked as insecure.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[Ma27]

@flokli @adisbladis is there any specific reason why this wasn't backported to release-20.09? I can do it by myself of course, I just want to make sure that there are no reasons against that which I may be missing :)

[adisbladis]

@Ma27 No reason, feel free to create a backport PR.

[Mic92]

For some reason it tries to import libvirt, even so we don't use it in nix-community

[nix-shell:~/git/infra]$ ./deploy
Traceback (most recent call last):
  File "/nix/store/6yf9ysc1k9bpiwfcpkw5gfy7hy15sr7d-nixops-1.7/bin/..nixops-wrapped-wrapped", line 5, in <module>
    from nixops import deployment
  File "/nix/store/vby2ym4vfwapvikwms26l1i7y6b8m0hg-nixops-1.7/lib/python2.7/site-packages/nixops/deployment.py", line 1281, in <module>
    _load_modules_from("backends")
  File "/nix/store/vby2ym4vfwapvikwms26l1i7y6b8m0hg-nixops-1.7/lib/python2.7/site-packages/nixops/deployment.py", line 1279, in _load_modules_from
    importlib.import_module("nixops." + dir + "." + module[:-3])
  File "/nix/store/yws041px65cq9l9s03jv3hv18wwkfmaz-python-2.7.18/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/nix/store/vby2ym4vfwapvikwms26l1i7y6b8m0hg-nixops-1.7/lib/python2.7/site-packages/nixops/backends/libvirtd.py", line 11, in <module>
    import libvirt
ImportError: No module named libvirt
Traceback (most recent call last):
  File "/nix/store/6yf9ysc1k9bpiwfcpkw5gfy7hy15sr7d-nixops-1.7/bin/..nixops-wrapped-wrapped", line 5, in <module>
    from nixops import deployment
  File "/nix/store/vby2ym4vfwapvikwms26l1i7y6b8m0hg-nixops-1.7/lib/python2.7/site-packages/nixops/deployment.py", line 1281, in <module>
    _load_modules_from("backends")
  File "/nix/store/vby2ym4vfwapvikwms26l1i7y6b8m0hg-nixops-1.7/lib/python2.7/site-packages/nixops/deployment.py", line 1279, in _load_modules_from
    importlib.import_module("nixops." + dir + "." + module[:-3])
  File "/nix/store/yws041px65cq9l9s03jv3hv18wwkfmaz-python-2.7.18/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/nix/store/vby2ym4vfwapvikwms26l1i7y6b8m0hg-nixops-1.7/lib/python2.7/site-packages/nixops/backends/libvirtd.py", line 11, in <module>
    import libvirt
ImportError: No module named libvirt

[flokli]

@Mic92 is this sure the right version of nixops, with that patch? I built nixops on nixpkgs-master, and get another hash at least.

[Mic92]

Yes. It was a false alarm. And old nixops version sneaked in a weird way.