Refactor Application shutdown using new Service, AsyncService interfaces

src/ripple_core/node/LevelDBBackendFactory.cpp

@@ -193,6 +193,11 @@ public:
         return m_batch.getWriteLoad ();
     }
 
+    void stopAsync ()
+    {
+        m_batch.stopAsync ();
+    }
+
     //--------------------------------------------------------------------------
 
     void writeBatch (NodeStore::Batch const& batch)
@@ -200,6 +205,11 @@ public:
         storeBatch (batch);
     }
 
+    void writeStopped ()
+    {
+        m_scheduler.scheduledTasksStopped ();
+    }
+
 private:
     size_t const m_keyBytes;
     NodeStore::Scheduler& m_scheduler;