To setup magnum easier, name based configuration is important.
This patch makes config file support trustee_domain_name and
trustee_domain_admin_name in trust section.
If name and id of trustee domain are provided by user, both
values are passed through into keystone.
Closes-Bug: #1581372
Change-Id: Ia691aca7c29a471f6ba36a1a371ec1edf830b365