Comment 5 for bug 1828543

Just for fun:
https://opendev.org/openstack/placement/src/branch/master/placement/util.py#L94
placement.util.json_error_formatter is the method that formats the http body to be the above mentioned.

The why is summarized here: http://specs.openstack.org/openstack/api-wg/guidelines/errors.html as referenced in placement code as well.