fix exception class to frontend
fix exception class to frontend

shaohua-zhang/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu