[AIRFLOW-3760] - Ensure that we pass the command to the Kubernetes Pod as a List

[PaulW]

Make sure you have checked all steps below.

Jira

• https://issues.apache.org/jira/browse/AIRFLOW-3760

Description

• AIRFLOW-2888 caused worker pod creation to fail, as we are not passing the command to kubernetes as a list item.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason: This fixes an issue created with a previous pull request.

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":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• 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.
  • All the public functions and the classes in the PR contain docstrings that explain what it does

Code Quality

• Passes flake8

[ashb]

This is not the right level to fix it, and splitting on space is error prone.

The correct way to fix this would be to make sure this stays as a list though all layers in think.

This also needs tests.

[timpharo]

This breaking change is affecting us too. From what I can see and have read from the description this is a contribution back for a breaking change that was made in #3740.
Looking through the original PR, the changes made that are causing issues with 'cmds' seems unrelated to the description of the original pull request and furthermore the original pull request doesn't have any tests, stating "Tests updated (but not functionally)".

As an open source project that to my knowledge is very well used now, I find it hard to believe that this kind of thing has been merged with comments outstanding such as "The airflow command is not passed as a string anymore. I need some help in doing this properly for the k8s executor most likely".

As the merge of #3740 has broken the K8 functionality, it seems that the correct action would be to revert those changes and re-implement with better testing in place.

[ashb]

Not disputing this is a problem, but PR#3760 is not yet included in an published release so that can't be the source of the issue.