Workaround for kubernetes-client version issue

[iameskild]

Fixes | Closes | Resolves #1147

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Changes introduced in this PR:

• Use list_namespace() instead of list_node() as a means of checking the kubernetes cluster created in stage 02 is up and running.

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[iameskild]

Integration tests pass with this change:
https://github.com/Quansight/qhub-integration-test/actions/runs/1945542740