### Jira https://issues.apache.org/jira/projects/AIRFLOW/issues/AIRFLOW-2797
### Description In GCP, it is possible to create Dataproc cluster with a custom image that includes user's pre-installed packages. It significantly reduces the startup time of the cluster. For more info see: https://cloud.google.com/dataproc/docs/guides/dataproc-images ### Tests Two tests added: - one checks assertion in case someone passes both `image_version` & `custom_image` - such a situation does not make sense from the configuration perspective - one check if `imageUri` is correctly set in `cluster_data` ### Commits - [ ] 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 - [ ] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff` [ Full content available at: https://github.com/apache/incubator-airflow/pull/3871 ] This message was relayed via gitbox.apache.org for [email protected]
