fix integration test MapReduceIT

1. Add byte array serde in RowWritable for Writable interface
2. Add ByteArrayAdapter for gson to serialize and deserialize byte array
3. Fix iterator in MapReduceIT.CountReduce
4. Fix index off-by-one issue in testDumpTableToHDFS
Merge pull request #194 from yaoshengzhe/fix_MapReduceIT

fix integration test MapReduceIT