Fix Netconf key elements serialization order (CiscoDevNet#363)

* Update for ydk core version 0.5.4

ydkgen/api_model.py

@@ -865,7 +865,7 @@ def get_properties(owned_elements):
 
     # first get the key properties
     key_props = [p for p in all_props if p.is_key()]
-    props.extend(sorted(key_props, key=lambda p:p. name))
+    props.extend(key_props)
 
     non_key_props = [p for p in all_props if not p.is_key()]
     props.extend(sorted(non_key_props, key=lambda p: p.name))