batch_writer: only parse args when invoked as script
batch_writer: only parse args when invoked as script

Closes issue #138

dongjoon-hyun/neon,dongjoon-hyun/neon,dongjoon-hyun/neon,NervanaSystems/neon,Jokeren/neon,Jokeren/neon,Bam4d/neon,coufon/neon-distributed,Jokeren/neon,coufon/neon-distributed,nhynes/neon,nhynes/neon,Bam4d/neon,NervanaSystems/neon,NervanaSystems/neon,NervanaSystems/neon,nhynes/neon,coufon/neon-distributed,Jokeren/neon,DougFirErickson/neon,Bam4d/neon,DougFirErickson/neon,DougFirErickson/neon