brick has duplicate conf entries in iser and iscsi

[Walt Boring]

in cinder/brick/iscsi/iscsi.py
                    cfg.StrOpt('volumes_dir',
                               default='$state_path/volumes',
                               help='Volume configuration file storage '
                                    'directory'),

in cinder/brick/iser/iser.py
                   cfg.StrOpt('volumes_dir',
                              default='$state_path/volumes',
                              help='Volume configuration file storage '
                                   'directory'

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/48124

[John Griffith (john-griffith)]

In progress here as part of another bug: https://review.openstack.org/#/c/48528/