[AIRFLOW-5048] Improve display of Kubernetes resources

[ms32035]

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Jira

• My PR addresses the following [Airflow Jira]
  • https://issues.apache.org/jira/browse/AIRFLOW-5048

Description

• Here are some details about my PR, including screenshots of any UI changes:

At the moment just a serialized class is displayed in task instance view. This PR improves string conversion

Tests

• My PR adds the following unit tests:

test_display_resources

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.

Code Quality

• Passes flake8

[andriisoldatenko]

self.request_memory can be None, may be check first?
same for self.limit_memory

[ms32035]

true, the test covers this, None to string is 'None'

[potiuk]

We've just merged GPU limits as well so you should add them.

[potiuk]

Tests fail on python 3.5

[potiuk]

I think now they will fail on python 3.6 I am afraid. You should use OrderedDict if you want to maintain order @ms32035

[ms32035]

I'll go for a simpler solution instead of trying to have dict ordering solution compatible with both 3.5 and 3.6

[ms32035]

@potiuk current test failures are not related to the change

[potiuk]

@ms32035 -> please rebase to master (but only after we merge #5703 as it fixes broken master due to dependency problem)

[dimberman]

@potiuk this all LGTM but I'll hold off unless you have any other concerns.