Add a TODO to remove Ironic related workaround

This patch adds a TODO to do not forget to remove temporary workaround
that ignores 'DOWN' Neutron port status for baremetal instance.

Related-Bug: #1599836

Change-Id: I71232e61e977999e8beb105824ad04d9120ad453
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index b151375..a0d6043 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -832,6 +832,7 @@
         # NOTE(vsaienko) With Ironic, instances live on separate hardware
         # servers. Neutron does not bind ports for Ironic instances, as a
         # result the port remains in the DOWN state.
+        # TODO(vsaienko) remove once bug: #1599836 is resolved.
         if CONF.service_available.ironic:
             p_status.append('DOWN')
         port_map = [(p["id"], fxip["ip_address"])