### Jira - [x] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. - [https://jira.apache.org/jira/browse/AIRFLOW-3069](https://jira.apache.org/jira/browse/AIRFLOW-3069)
### Description - [x] Here are some details about my PR, including screenshots of any UI changes: The output of the process spawned by `S3FileTransformOperator` is not properly decoded, which makes reading logs rather difficult. Additionally, the `stderr` stream is only shown when process exit code is not equal to `0`. I would like to propose the following changes to `S3FileTransformOperator`: - Send both output streams (stdout & stderr) to the logger, regardless of the outcome (if any data is present) - Decode the output, so that new lines can be displayed correctly. - Include process exit code in the exception message, if the process fails. ### Tests - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason: I've added a separate case for testing `transform_script` with output present. Since logging is essential in this case, the test checks if a valid message was passed to the logging module. ### Commits - [x] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)": 1. Subject is separated from body by a blank line 1. Subject is limited to 50 characters (not including Jira issue reference) 1. Subject does not end with a period 1. Subject uses the imperative mood ("add", not "adding") 1. Body wraps at 72 characters 1. Body explains "what" and "why", not "how" ### Documentation - [x] In case of new functionality, my PR adds documentation that describes how to use it. - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added. ### Code Quality - [x] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff` [ Full content available at: https://github.com/apache/incubator-airflow/pull/3914 ] This message was relayed via gitbox.apache.org for [email protected]
