Detect new images added to the default image directory.

* Images can be present before the server starts or while it is running
* Images are recorded in the database

gns3server/compute/base_manager.py

@@ -506,7 +506,7 @@ class BaseManager:
         """
 
         try:
-            return list_images(self._NODE_TYPE)
+            return await list_images(self._NODE_TYPE)
         except OSError as e:
             raise ComputeError(f"Can not list images {e}")