nixos/test/test-driver: Class-ify the test driver

This commit encapsulates the involved domain into classes and
defines explicit and typed arguments where untyped dicts where used.

It preserves backwards compatibility through legacy wrappers.

nixos/lib/testing-python.nix

@@ -43,7 +43,8 @@ rec {
         from pydoc import importfile
         with open('driver-symbols', 'w') as fp:
           t = importfile('${testDriverScript}')
-          test_symbols = t._test_symbols()
+          d = t.Driver([],[],"")
+          test_symbols = d.test_symbols()
           fp.write(','.join(test_symbols.keys()))
         EOF
       '';
@@ -188,14 +189,6 @@ rec {
           --set startScripts "''${vmStartScripts[*]}" \
           --set testScript "$out/test-script" \
           --set vlans '${toString vlans}'
-
-        ${lib.optionalString (testScript == "") ''
-          ln -s ${testDriver}/bin/nixos-test-driver $out/bin/nixos-run-vms
-          wrapProgram $out/bin/nixos-run-vms \
-            --set startScripts "''${vmStartScripts[*]}" \
-            --set testScript "${pkgs.writeText "start-all" "start_all(); join_all();"}" \
-            --set vlans '${toString vlans}'
-        ''}
       '');
 
   # Make a full-blown test