Fix broken links to testgrid dashboard

[letmerecall]

What type of PR is this:

/kind documentation

What this PR does / why we need it:

Fixes a bunch of broken link to testgrid dashboard

Which issue(s) this PR fixes:

Fixes #2304

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[cpanato]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, letmerecall

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