'Add servers to private network
:param network_id: Private Network ID
:rtype: ``str``
:param server_ids: List of server IDs
:rtype: ``list`` of ``str``
:return: List of attached servers
:rtype: ``dict``'

def ex_add_private_network_server(self, network_id, server_ids):

    body = {'servers': server_ids}
    response = self.connection.request(action=('/private_networks/%s/servers' % network_id), data=body, method='POST')
    return response.object
