Return the container root directory. Starting with systemd 219, new
    images go into /var/lib/machines.

def _root(name='', all_roots=False):
    '''
    Return the container root directory. Starting with systemd 219, new
    images go into /var/lib/machines.
    '''
    if _sd_version() >= 219:
        if all_roots:
            return [os.path.join(x, name)
                    for x in ('/var/lib/machines', '/var/lib/container')]
        else:
            return os.path.join('/var/lib/machines', name)
    else:
        ret = os.path.join('/var/lib/container', name)
        if all_roots:
            return [ret]
        else:
            return ret