[schema] store default attribute values in a Bytes field, allowing python objects as default values Notes: * Binary objects grow two methods * we depend on a newer yams version * the code is quite simplified as a result of the whole change * a very old and nasty bug where bool(default values) evaluating to False not being properly migrated is killed Closes #2414591.

sync_schema_props_perms('cw_source', syncprops=False)
if schema['BigInt'].eid is None:
    add_entity_type('BigInt')