[test minor] Use `process.argv[0]` when spawning processes

Previous implementation used `node`.

test/helpers.js

@@ -43,11 +43,12 @@ exports.assertSystemConf = function (options) {
         });
       }
       
-      spawn('node', [options.script].concat(options.argv), { env: env })
+      spawn(process.argv[0], [options.script].concat(options.argv), { env: env })
         .stdout.once('data', this.callback.bind(this, null));
     },
     "should respond with the value passed into the script": function (_, data) {
       assert.equal(data.toString(), 'foobar');
     }
   }
-}
+}
+