tests/vmTest: fix and de-duplicate code

Ironically, I did not properly test that I had made the local and remote
tests distinct. So the exampleFlake was hardcoded to 'local' only.  This
meant that building local and remote tests would return the same
results. This commit fixes that. Additionally, I've made
tests/vmTests/common.nix to deduplicate some of the code between nodes.

tests/vmTest/common.nix

@@ -0,0 +1,14 @@
+# Configuration that will be added to both the nixinatee node and the nixinator
+# node.
+{ inputs }:
+{
+  nix = {
+    extraOptions =
+      let empty_registry = builtins.toFile "empty-flake-registry.json" ''{"flakes":[],"version":2}''; in
+      ''
+        experimental-features = nix-command flakes
+        flake-registry = ${empty_registry}
+      '';
+    registry.nixpkgs.flake = inputs.nixpkgs;
+  };
+}

tests/vmTest/default.nix

@@ -22,6 +22,8 @@ let
     ((import (path + "/flake.nix")).outputs (inputs // {self = r;}));
   in
     r;
+  mkNixinateTest = buildOn:
+    let
       exampleFlake = pkgs.writeTextFile {
         name = "nixinate-example-flake";
         destination = "/flake.nix";
@@ -38,7 +40,7 @@ let
                       _module.args.nixinate = {
                         host = "nixinatee";
                         sshUser = "nixinator";
-                    buildOn = "local"; # valid args are "local" or "remote"
+                        buildOn = "${buildOn}"; # valid args are "local" or "remote"
                       };
                     }
                   ];
@@ -54,32 +56,29 @@ let
       };
       deployScript = inputs.self.nixinate.${pkgs.hostPlatform.system} (callLocklessFlake "${exampleFlake}" { nixpkgs = inputs.nixpkgs; });
       exampleSystem = (callLocklessFlake "${exampleFlake}" { nixpkgs = inputs.nixpkgs; }).nixosConfigurations.nixinatee.config.system.build.toplevel;
-  mkNixinateTest = buildOn: makeTest {
+    in
+    makeTest {
       nodes = {
         nixinatee = { ... }: {
           imports = [
             ./nixinateeBase.nix
+            (import ./common.nix { inherit inputs; })
           ];
           virtualisation = {
             writableStore = true;
+            additionalPaths = [] ++ pkgs.lib.optional (buildOn == "remote") (allDrvOutputs exampleSystem);
           };
         };
         nixinator = { ... }: {
+          imports = [
+            (import ./common.nix { inherit inputs; })
+          ];
           virtualisation = {
             additionalPaths = [
               (allDrvOutputs exampleSystem)
             ]
               ++ pkgs.lib.optional (buildOn == "remote") exampleFlake;
           };
-        nix = {
-          extraOptions =
-            let empty_registry = builtins.toFile "empty-flake-registry.json" ''{"flakes":[],"version":2}''; in
-            ''
-              experimental-features = nix-command flakes
-              flake-registry = ${empty_registry}
-            '';
-          registry.nixpkgs.flake = inputs.nixpkgs;
-        };
         };
       };
       testScript =