'Unmanage volume.
For a full list of available parameters, please refer to the official
API reference:
https://developer.openstack.org/api-ref/block-storage/v2/#unmanage-volume'

def unmanage_volume(self, volume_id):

    post_body = json.dumps({'os-unmanage': {}})
    (resp, body) = self.post(('volumes/%s/action' % volume_id), post_body)
    self.expected_success(202, resp.status)
    return rest_client.ResponseBody(resp, body)
