вот такое отработало:
// get current jmeter script's directory
def baseDir = FileServer.getFileServer().getBaseDir();
def configDir = baseDir + "/" + vars.get("CONFIG_DIR");
// Create file objects
def artist_file = new File(configDir + "/artist_ids.csv");
// Reading contents of files to arrays
def artist_ids =artist_file.readLines();
props.put("artist_ids", artist_ids);
def r = new Random();
index = r.nextInt(artist_ids.size());
artist_id = artist_ids.get(index);
log.info("@@@@@@@@@@=" + artist_id);