Decorators could simplify using different services and endpoints.

New ex_list_all_volumes

from decorators import cinder

# ...

    @cinder
    def ex_list_all_volumes(self):
        """
        List all volumes from all tenants of a user
        """
        resp = self.connection.request(
            '/volumes/detail?all_tenants=1',
            method='GET')
        return self._to_volumes(resp.object, glance=True)

Old ex_list_all_volumes

    def ex_list_all_volumes(self):
        """
        List all volumes from all tenants of a user
        """
        lc_conn = self.connection
        if not lc_conn.service_catalog:
            lc_conn.get_service_catalog()
        #Change base_url, make request, update base_url
        if lc_conn._ex_force_base_url:
            old_endpoint = lc_conn._ex_force_base_url
        else:
            old_endpoint = lc_conn.get_endpoint()
        try:
            new_service = lc_conn.service_catalog.get_endpoint(
                service_type='volume', name='cinder',
                region=lc_conn.service_region)
            lc_conn._ex_force_base_url = new_service['publicURL']
            server_resp = lc_conn.request(
                '/volumes/detail?all_tenants=1',
                method='GET')
            return self._to_volumes(server_resp.object, glance=True)
        finally:
            lc_conn._ex_force_base_url = old_endpoint