Issue description

virt-manager fails to load and instead produces the error "Namespace LibvirtGLib not available"

Traceback (most recent call last):
  File "/nix/store/b8na689bifds8z2xg1bragbw54mznppa-virt-manager-2.1.0/share/virt-manager/virt-manager", line 17, in <module>                                                                   
    gi.require_version('LibvirtGLib', '1.0')
  File "/nix/store/kiw47xswi1041sbvbgrlfy0xs0zlwyvk-python3.7-pygobject-3.30.4/lib/python3.7/site-packages/gi/__init__.py", line 129, in require_version                                        
    raise ValueError('Namespace %s not available' % namespace)
ValueError: Namespace LibvirtGLib not available

I'm aware of #33754 and #34000. I have the changes in the merged commit. Yet, I receive the error.

Steps to reproduce

1. Install virt-manager
2. Open a terminal and run virt-manager

Technical details

• system: "x86_64-linux"
• host os: Linux 4.14.104, NixOS, 19.09.git.27cb066 (Loris)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2
• channels(root): "nixos-19.09pre171582.26d8a8c0eb2"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

NOTE: My nixpkgs is not as shown above but rather a clone of this repo at commit 27cb066