Get encrypted administrator password for a Windows instance.

        :type instance_id: string
        :param instance_id: The identifier of the instance to retrieve the
                            password for.

def get_password_data(self, instance_id):
        """
        Get encrypted administrator password for a Windows instance.

        :type instance_id: string
        :param instance_id: The identifier of the instance to retrieve the
                            password for.
        """

        params = {'InstanceId' : instance_id}
        rs = self.get_object('GetPasswordData', params, ResultSet, verb='POST')
        return rs.passwordData