Create a minimal system configuration for use in a container.
    @param basedir: The directory where the configuration files should be placed as bytes.
    @param mountdir: If present, bind mounts to the configuration files will be added below
        this path (given as bytes).

def setup_container_system_config(basedir, mountdir=None):
    """Create a minimal system configuration for use in a container.
    @param basedir: The directory where the configuration files should be placed as bytes.
    @param mountdir: If present, bind mounts to the configuration files will be added below
        this path (given as bytes).
    """
    etc = os.path.join(basedir, b"etc")
    if not os.path.exists(etc):
        os.mkdir(etc)

    for file, content in CONTAINER_ETC_FILE_OVERRIDE.items():
        # Create "basedir/etc/file"
        util.write_file(content, etc, file)
        if mountdir:
            # Create bind mount to "mountdir/etc/file"
            make_bind_mount(
                os.path.join(etc, file), os.path.join(mountdir, b"etc", file), private=True)

    os.symlink(b"/proc/self/mounts", os.path.join(etc, b"mtab"))