jsonutils.to_primitive does not follow the protocol required by json.dump

[Balazs Gibizer]

"If specified, default should be a function that gets called for objects that can’t otherwise be serialized. It should return a JSON encodable version of the object or raise a TypeError. If not specified, TypeError is raised." [1]

So jsonutils.to_primitive[2], that is used as default in jsonutils.dumps, is broken as
i) it returns the same object if the object is not serializable instead of raising TypeError
ii) it warns the user of the lib that ValueError will be raised from 3.0 instead of TypeError
iii) oslo.serialization 3.0 is released without changing that warning to a real exception raise

[1] https://docs.python.org/3.6/library/json.html#json.dump
[2] https://github.com/openstack/oslo.serialization/blob/301b0cb54c82a837913dc9d71e792eb4df9b7273/oslo_serialization/jsonutils.py#L191

[Ben Nemec (bnemec)]

It looks like we need to address Glance before we remove this. I see the warning occurring in their logs on a regular basis: http://logstash.openstack.org/#dashboard/file/logstash.json?query=message%3A%5C%22will%20raise%20ValueError%5C%22

[Ben Nemec (bnemec)]

I also see some log entries from an ironic py38 job and a nova lower-constraints job.