[FSTORE-1567] Fix login error messages (#364)

Author: aversey

python/hopsworks_common/connection.py

@@ -457,7 +457,8 @@ def close(self) -> None:
         """
         from hsfs import engine
 
-        OpenSearchClientSingleton().close()
+        if OpenSearchClientSingleton._instance:
+            OpenSearchClientSingleton().close()
         client.stop()
         engine.stop()
         self._feature_store_api = None