Barbican should list more than 10 secrets

Castellan only passes limited parameters to the list operation and doesn't include a size limit: https://github.com/openstack/castellan/blob/master/castellan/key_manager/barbican_key_manager.py#L592

However, python-barbicanclient includes a default limit of 10 if None is specified:
https://github.com/openstack/python-barbicanclient/blob/41f4e3b0ac88158150785ce3438c211b7d758336/barbicanclient/v1/secrets.py#L537

This means you can only get 10 secrets from Barbican. Other parameters should be passed to either better support paging in Castellan, or to have Castellan increase the number of requests from Barbican.