make a test case just for login in gnome

[worldofpeace]

Describe the bug
The two tests we have for gnome are basically gnome-terminal tests.
It logs in and launches gnome-terminal. Nothing more nothing less.
But there's a whole lot of other things we need to make sure work in gnome like:

• adding a user (I know ew, this is nixos but imperative users are still a thing.)
• login
• logout
• switch user
• reboot
• more...? or various permutations of this

This is a test used in fedora for gnome (and also plasma) for login that could be used as a reference:

• https://pagure.io/fedora-qa/os-autoinst-distri-fedora/blob/master/f/tests/desktop_login.pm

I will also mention that we're lacking a lot of ability in the testing driver to do these things.

Links to gnome tests:

• https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/gnome3-xorg.nix
• https://github.com/NixOS/nixpkgs/blob/master/nixos/tests/gnome3.nix

[stale]

I marked this as stale due to inactivity. → More info