nixos/lib/qemu-flags: rename to qemu-common

The current name is misleading: it doesn't contain cli arguments,
but several constants and utility functions related to qemu.
This commit also removes the use of `with import ...` for clarity.

nixos/lib/testing-python.nix

@@ -217,7 +217,7 @@ rec {
       nodes = qemu_pkg:
         let
           build-vms = import ./build-vms.nix {
-            inherit system pkgs minimal specialArgs;
+            inherit system lib pkgs minimal specialArgs;
             extraConfigurations = extraConfigurations ++ [(
               {
                 virtualisation.qemu.package = qemu_pkg;
@@ -257,7 +257,6 @@ rec {
         inherit test driver driverInteractive nodes;
       };
 
-
   abortForFunction = functionName: abort ''The ${functionName} function was
     removed because it is not an essential part of the NixOS testing
     infrastructure. It had no usage in NixOS or Nixpkgs and it had no designated