The issue is that bridge_interface is None by default ({vlan,flat}_interface flag is None by default and nova-manage uses flag if you don't specify a bridge interface when creating network).
Then ensure_vlan_bridge (and ensure_vlan) happily try to use "None" as the bridge interface name.
The issue is that bridge_interface is None by default ({vlan, flat}_interface flag is None by default and nova-manage uses flag if you don't specify a bridge interface when creating network).
Then ensure_vlan_bridge (and ensure_vlan) happily try to use "None" as the bridge interface name.