### Jira - [x] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title.
### Description - [x] Here are some details about my PR, including screenshots of any UI changes: Both Deploy and Delete operators interact with Google Cloud Functions to manage functions. Both are idempotent and make use of GcfHook - hook that encapsulates communication with GCP over GCP API. Invoke operator is also in the works, but it waits for alpha IAM functionality that will soon be available and helps with protecting invoke operation. Part of this commit message is also Body Field Validator that is meant to be reusable (but for now is an integral part of GCF operators). It will be separated out into utils in one of the subsequent Pull Requests where it will be reused in other operators (GCE ones) ### Tests - [X] My PR adds the following unit tests * GcfFunctionDeployTest class * GcfFunctionDeleteTest class 63 tests in total (includes parameterised test) ### 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/3969 ] This message was relayed via gitbox.apache.org for [email protected]
