Writables need instantiation similar to InputFormats

[dvryaboy]

With Raghu's refactoring, we can set the inputFormat and outputFormat as follows:

job.setInputFormatClass(
  LzoProtobufB64LineInputFormat.getInputFormatClass(MyProtobufClass.class, conf)
);

We need to do the same for Writables, as this: job.setOutputValueClass(ThriftWritable.class); doesn't work.