Include name of parent type of each type on 'qom-list-types' output.

Without this, there's no way to figure out the parents of a given type
without making additional 'qom-list-types' queries.

In addition to the test case for the new feature, update the
abstract-interface test case to use the new field and avoid the
"qom-list-types implements=object" trick.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170707122215.8819-4-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>