add support for AWS Data Pipeline's GetPipelineDefinition endpoint

http://docs.aws.amazon.com/datapipeline/latest/APIReference/API_GetPipelineDefinition.html
add support for AWS Data Pipeline's QueryObjects endpoint

http://docs.aws.amazon.com/datapipeline/latest/APIReference/API_QueryObjects.html
add support for AWS Data Pipeline's DescribeObjects endpoint

http://docs.aws.amazon.com/datapipeline/latest/APIReference/API_DescribeObjects.html
Merge pull request #2129 from mattgillooly/add_aws_data_pipeline_get_pipeline_definition

support for additional AWS Data Pipeline API endpoints