NodeStore improvements:

* Add Backend::verify API for doing consistency checks
* Add Database::close so caller can catch exceptions
* Improved Timing test for NodeStore creates a simulated workload

test/config-example.js

@@ -56,7 +56,8 @@ exports.servers = {
                            'admin = allow',
                            'protocol = ws'),
 
-    'node_db': 'type=memory'
+    'node_db': lines('type=memory',
+                     'path=integration')
   }
 };