add log of load freeze_info/global_merge_info/zone_merge_info and defence of scn_revert

src/share/ob_freeze_info_proxy.cpp

@@ -165,6 +165,7 @@ int ObFreezeInfoProxy::get_freeze_info_larger_or_equal_than(
       }
     }
   }
+  LOG_INFO("finish load_freeze_info", KR(ret), K_(tenant_id), K(sql));
   return ret;
 }