nixos/tests: expose both the interactive and non-interactive driver

For a lot of the work the non-interactive drivers are enough and it is
probably a good idea to keep it accessible for debugging without
touching the Nix expression.

nixos/lib/testing-python.nix

@@ -172,7 +172,8 @@ rec {
       else
         test // {
           inherit nodes test;
-          driver = driver testDriverInteractive;
+          driver = driver testDriver;
+          driverInteractive = driver testDriverInteractive;
         };
 
   runInMachine =