Shell executor logs through testing.T in upgrade tests

[mgencur]

Similar to https://github.com/knative/serving/pull/14495

Fixes #

Proposed Changes

• Print logs from shell executor to testing.T so that the logs can be found within test scope

Release Note

[knative-prow[bot]]

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[knative-prow-robot]

PR needs rebase.

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[matzew]

@mgencur can you rebase?

[github-actions[bot]]

This Pull Request is stale because it has been open for 90 days with no activity. It will automatically close after 30 more days of inactivity. Reopen with /reopen. Mark as fresh by adding the comment /remove-lifecycle stale.

[houshengbo]

Let me ping @mgencur one more time to see if he can rebase and fix the CI issues with this PR.