Use entrypoint and cmd for play kube

[bziemons]

The image's ENTRYPOINT and CMD were not handled correctly and overriding them in the container yaml specification was not supported for the entrypoint (called command as the Kubernetes field, see https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#notes).
If I haven't overlooked anything, this PR should implement the scheme in the link above.

Closes #8428

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[oleastre]

This is probably a duplicate of #8666.

[bziemons]

This is probably a duplicate of #8666.

thanks for the heads-up. I wasn't aware of that because it doesn't mention the issue #8428. This was a quick fix for me so I do not mind if this just gets closed. I haven't touched the tests yet and they seem to expect something else. I have however rolled this change out to my server to not hang behind on a rolling distro.