Add --fallback-requisite-zones command line argument

[pwschuurman]

What type of PR is this?
/kind bug

What this PR does / why we need it:
Fixes Regional Persistent Disk provisioning on GKE Autopilot clusters when there is only 0 or 1 zones available across nodes in the cluster.

Which issue(s) this PR fixes:
Fixes #1531

Special notes for your reviewer:
This changes the behavior for Regional PD CreateVolume calls that have only one preferred topology. Previously, if a Regional PD was provisioned with a single preferredTopology (zone), and a list of requisite topologies (Zone), the secondary zone would be selected at random. This differed from the logic in the external provisioner, which picks the secondary zone deterministically, based on the primary preferred topology.

We don't expect this scenario to occur in practice, since the external provisioner will either pass in in at least two preferred topologies, or only one (and currently will fail, unless the --fallback-requisite-zones flag is provided). So it is safe to change this behavior as there should not be any real world scenarios relying on the random selection of the secondary zone that would be broken by a change to determinism.

Does this PR introduce a user-facing change?:

Add --fallback-requisite-zones flag to allow disk provisioning to fallback to a default set of zones when there are an insufficient number of zones available in a passed in requisite topology in CreateVolume.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pwschuurman

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[pwschuurman]

/assign @msau42

[pwschuurman]

/cc @amacaskill

[amacaskill]

/cc @amacaskill

This LGTM. All the test cases you added helps make it clear this still works with volume cloning. The only testcase I didn't see was regional -> regional volume cloning with --fallback-requisite-zones specified / used.

[pwschuurman]

/cc Alexis MacAskill

This LGTM. All the test cases you added helps make it clear this still works with volume cloning. The only testcase I didn't see was regional -> regional volume cloning with --fallback-requisite-zones specified / used.

Thanks, added an extra test case for regional -> regional volume cloning.

[msau42]

/lgtm

[pwschuurman]

/cherrypick release-1.12

[k8s-infra-cherrypick-robot]

@pwschuurman: new pull request created: #1542

In response to this:

/cherrypick release-1.12

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