Fix KubernetesExecutor import is broken in webserver - Airflow 1.10.11

[hienpham2tiki]

Wrong KubernetesExecutor import path causes User can not trigger dag task run in the UI in airflow 1.10.11

---

Read the Pull Request Guidelines for more information.
In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst)
Here are some useful points:

• Pay attention to the quality of your code (flake8, pylint and type annotations). Our pre-commits will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
• Consider using Breeze environment for testing locally, it’s a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: [email protected]
  Slack: https://apache-airflow-slack.herokuapp.com/

[mik-laj]

We have one more problem here. All import paths should be backward compatible. After moving the modules, we should create new modules with references to new locations.
Please look here for an example: https://github.com/apache/airflow/tree/master/airflow/contrib/operators

Your change only partially solves the problem, because other users can still expect KubernetesExecutor in this module and we should handle that too.

[hienpham2tiki]

Updated, cc @mik-laj

[dimberman]

#10084 fixed here