node type parent interfaces are ignored

Validating failed on interfaces which are defined by parents types

Example is failing with "Unknown interface preconfigure"

node_types:
  openstack.nodes.Root:
    derived_from: tosca.nodes.Root
    interfaces:
      Prepare:
        type: openstack.interfaces.node.Prepare
    <...>

  openstack.nodes.Server:
    derived_from: openstack.nodes.Root
    <...>

interface_types:
  openstack.interfaces.node.Prepare:
    description: >
      The lifecycle interfaces define the essential<...>
    derived_from: tosca.interfaces.Root
    preconfigure:
      description: Operation to pre-configure the node.