private static void addTableCell(StringBuilder sb, String colStart, String colEnd, String cellValue) {
        sb.append("  <td>").append(colStart).append(cellValue).append(colEnd).append("</td>\n");
    }
Used in unit testing to verify events generated.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/EventLog.java