Create Qemu VM working directories if required

    :param int max_qemu_id: Number of directories to create
    :param str output_dir: Output directory
    :param str topology_name: Topology name

def make_qemu_dirs(max_qemu_id, output_dir, topology_name):
    """
    Create Qemu VM working directories if required

    :param int max_qemu_id: Number of directories to create
    :param str output_dir: Output directory
    :param str topology_name: Topology name
    """
    if max_qemu_id is not None:
        for i in range(1, max_qemu_id + 1):
            qemu_dir = os.path.join(output_dir, topology_name + '-files',
                                    'qemu', 'vm-%s' % i)
            os.makedirs(qemu_dir)