add support for shared kind clusters

[sdowell]

this change adds support to run kind clusters with a shared test environment. This can be run either sequentially or in parallel. The clusters are created at the beginning of the suite, reused between tests, and deleted at the end of the suite.

This is intended to:

• Speed up the presubmit jobs by reducing time spent creating kind clusters
• Make it easier to run tests with a shared test environment (e.g. reproducing test cleanup issues locally)
• Shift-left the shared environment testing to the presubmits so issues with test cleanup can be found before reaching periodics

It occurred to me while implementing this that we could use the same approach for the GKE testing, where we treat a set of GKE clusters as a shared pool in the tests. This approach could potentially replace the test group configuration, which would simplify the prow configuration. For now this does not make any changes to how GKE shared tests are run.

[google-oss-prow[bot]]

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

[sdowell]

/cc @karlkfi /cc @nan-yu /test all

[sdowell]

/test all

[sdowell]

/test all

[sdowell]

/test all

[sdowell]

Pulled out the kubeconfig changes as a separate PR: https://github.com/GoogleContainerTools/kpt-config-sync/pull/238

[sdowell]

/test all

[sdowell]

/retest

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nan-yu

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[sdowell]

/retest