chore(test): Fixed namespace in tests

[hbelmiro]

This PR replaces the ${NAMESPACE} variable with kubeflow.
For some reason, some tests were being skipped and started to run when I added the namespace. That required me to forward ports and change one test.

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[google-oss-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[hbelmiro]

@HumairAK @chensun can one of you guys PTAL?

[HumairAK]

/approve

[google-oss-prow]

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[DharmitD]

/lgtm