Display <none> when port is empty.

[xiangpengzhao]

What this PR does / why we need it:
If container ports are not specified, kubectl describe displays <none> instead of empty.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

Release note:

NONE

[k8s-reviewable]

This change is 

[k8s-ci-robot]

Hi @xiangpengzhao. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with @k8s-bot ok to test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[fabianofranz]

@k8s-bot ok to test

[fabianofranz]

/lgtm
/approve

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabianofranz, xiangpengzhao

Needs approval from an approver in each of these OWNERS Files:

• pkg/printers/OWNERS [fabianofranz]

You can indicate your approval by writing /approve in a comment
You can cancel your approval by writing /approve cancel in a comment

[k8s-github-robot]

Automatic merge from submit-queue (batch tested with PRs 41903, 45311, 45474, 45472, 45501)