Lists all users within the tenant.

def user_list(self, params=None):
        """Lists all users within the tenant."""

        uri = 'openstack/users'
        if params:
            uri += '?%s' % urllib.urlencode(params)

        resp, body = self.get(uri)
        self.expected_success(200, resp.status)
        body = json.loads(body)
        return rest_client.ResponseBody(resp, body)