Fix ssh options in e2e framework

[L3n41c]

What does this PR do?

Fix the invocation of ssh in the e2e tests framework. Make a proper distinction between the SendEnv option (to propagate the current value of a local environment variable) and SetEnv option (to set an environment variable to a specific value on the remote host).

Motivation

Some versions of ssh don’t support passing a value with SendEnv.

Additional Notes

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

Validate that e2e tests are still passing.

Reviewer's Checklist

• [ ] If known, an appropriate milestone has been selected; otherwise the Triage milestone is set.
• [ ] Use the major_change label if your change either has a major impact on the code base, is impacting multiple teams or is changing important well-established internals of the Agent. This label will be use during QA to make sure each team pay extra attention to the changed behavior. For any customer facing change use a releasenote.
• [ ] A release note has been added or the changelog/no-changelog label has been applied.
• [ ] Changed code has automated tests for its functionality.
• [ ] Adequate QA/testing plan information is provided if the qa/skip-qa label is not applied.
• [ ] At least one team/.. label has been applied, indicating the team(s) that should QA this change.
• [ ] If applicable, docs team has been notified or an issue has been opened on the documentation repo.
• [ ] If applicable, the need-change/operator and need-change/helm labels have been applied.
• [ ] If applicable, the k8s/<min-version> label, indicating the lowest Kubernetes version compatible with this feature.
• [ ] If applicable, the config template has been updated.

[L3n41c]

SetEnv has been introduced in OpenSSH 7.7 and the version used in the CI doesn’t support it. :-(