[migration] Skip virtual rtypes when adding relation definition through add_cube
Virtual rtypes should be skipped as they are added dynamically on loading
schema. Those are skipped by e.g. schema serialisation or add_entity_type, do
the same thing here.
.. _appobject_module:
:mod:`cubicweb.appobject`
=========================
.. automodule:: cubicweb.appobject
.. autoclass:: AppObject
:show-inheritance:
:members: