code: def samtoolsMpileup(outFile, referenceFile, alignmentFile, executor):
      
      executor.execute(
          'samtools mpileup -u -v -f %s %s > %s' %
          (referenceFile, alignmentFile, outFile))
docs: Use samtools mpileup to generate VCF.
  
      @param outFile: The C{str} name to write the output to.
      @param referenceFile: The C{str} name of the FASTA file with the reference
          sequence.
      @param alignmentFile: The C{str} name of the SAM or BAM alignment file.
      @param executor: An C{Executor} instance.