python2Packages.nixpart0: fix build

[pbogdan]

Motivation for this change

While AFAICT not used directly in nixpkgs the package is used for provisioning new servers in nixops' Hetzner module.

This PR contains a collection of fixes for the package's dependencies to unblock its build. Closes #86403.

This branch contains the same commits as in #86403 (comment) just rebased onto more recent master.

If accepted I will make a backport PR to 20.03 as well as per the discussion on the linked issue.

/cc @nh2
/cc @kolloch @mkg20001 who might still be interested as well

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.

[pbogdan]

@GrahamcOfBorg build python2Packages.nixpart0

[nh2]

One request:

Please put a comment on each patch / fetchpatch that says why we need it (ideally also linking to the issue where we found the bug).

Beyond that, I have already tested this on 20.03.

[pbogdan]

Thanks! I added a brief note to each patch (mirroring the commit message) with a link to the issue as well. Let me know if that looks good or if there's anything else you would like me to amend.

[aszlig]

@pbogdan: Thanks a lot, building and merging in a moment.