code: public CreatePipelineResponse createPipeline(
              String pipelineName, String sourceBucket, String targetBucket, int capacity) {
          return createPipeline(pipelineName, null, sourceBucket, targetBucket, capacity);
      }
docs: Creates a pipeline which enable you to perform multiple transcodes in parallel.
  
  @param pipelineName The name of the new pipeline.
  @param sourceBucket The name of source bucket in Bos.
  @param targetBucket The name of target bucket in Bos.
  @param capacity     The concurrent capability of the new pipeline.