Automated cherry pick of #779

[JoshVanL]

Cherry pick of #779 on release-0.6.

779: Don't close closed channel in tunnel

[jetstack-bot]

@JoshVanL: All 'parent' PRs of a cherry-pick PR must have one of the "release-note" or "release-note-action-required" labels, or this PR must follow the standard/parent release note labeling requirement.

The following parent PRs have neither the "release-note" nor the "release-note-action-required" labels: #779. Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[jetstack-bot]

@JoshVanL: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[jetstack-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JoshVanL

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/jetstack/tarmak/blob/release-0.6/OWNERS)~~ [JoshVanL] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[JoshVanL]

/assign @simonswine