[H2] Fix to cleanly close feature database

Author: alexrobin

sensorhub-datastore-h2/src/main/java/org/sensorhub/impl/datastore/h2/MVFeatureDatabase.java

@@ -100,6 +100,9 @@ protected void doStop() throws SensorHubException
     {
         if (mvStore != null) 
         {
+            // must call commit first to make sure kryo persistent class resolver
+            // is updated before we serialize it again in close
+            mvStore.commit();
             mvStore.close();
             mvStore = null;
         }