check valid resource version for nb_api

Change-Id: I86a47aee3bdb794328cc4958f91b474c854a9ebc
Closes-bug: #1651439

dragonflow/common/utils.py

@@ -43,6 +43,20 @@ def get_vhu_sockpath(sock_dir, port_id):
         (n_const.VHOST_USER_DEVICE_PREFIX + port_id)[:14])
 
 
+def is_valid_version(old_obj, new_obj):
+    if not old_obj:
+        return True
+
+    if new_obj.get('version') > old_obj.get('version'):
+        return True
+    elif new_obj.get('version') == old_obj.get('version'):
+        return False
+    else:
+        LOG.debug("new_obj has an old version, new_obj: %s, old_obj: %s",
+                  new_obj, old_obj)
+        return False
+
+
 def load_driver(driver_cfg, namespace):
     try:
         # Try to resolve by alias