synchronized void closeFileTarget() {
        try {
            logTarget.close();
        }
        catch (RuntimeException e) {
            LogRecord r = new LogRecord(Level.WARNING, "Unable to close log");
            r.setThrown(e);
            emergencyLog(r);
        }
    }
Closes the target log file, if there is one
vespalog/src/main/java/com/yahoo/log/VespaLogHandler.java