Fix container image short names for OpenShift compatibility

[anik120]

Description of the change:

Replace short image names (nginx:, bitnami/nginx:, repo/image:) with fully qualified names (docker.io/) in tests to resolve failures in OpenShift clusters with container image short name enforcement enabled.

Motivation for the change:

Architectural changes:

Testing remarks:

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Bug fixes are accompanied by regression test(s)
• e2e tests and flake fixes are accompanied evidence of flake testing, e.g. executing the test 100(0) times
• tech debt/todo is accompanied by issue link(s) in comments in the surrounding code
• Tests are comprehensible, e.g. Ginkgo DSL is being used appropriately
• Docs updated or added to /doc
• Commit messages sensible and descriptive
• Tests marked as [FLAKE] are truly flaky and have an issue
• Code is properly formatted

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: grokspawn

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[grokspawn]

I would prefer a title that was less downstream-y, like "fully-specify image pullspec source registries for compatibility with non-docker container environments".