Skip validation for clusterCIDR in node ipam controller.

[grayluck]

What type of PR is this?
/kind bug

What this PR does / why we need it:
When CIDRAllocationType == ipam.CloudAllocatorType, clusterCIDR will not be used but decided at the cloud provider side. Thus we should not validate against clusterCIDR, and allow clusters with an nil clusterCIDR.

clusterCIDR is passed down from kube_env CLUSTER_IP_RANGE to the flag --cluster-cidr.

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

None

/assign @freehan

[k8s-ci-robot]

Hi @grayluck. Thanks for your PR.

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[grayluck]

/priority backlog

[grayluck]

/assign @freehan

[grayluck]

/priority important-soon

[freehan]

/ok-to-test

[grayluck]

/retest

[freehan]

/approve
/lgtm

[freehan]

/assign @bowei for approval

[k8s-ci-robot]

@freehan: GitHub didn't allow me to assign the following users: for, approval.

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In response to this:

/assign @bowei for approval

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[grayluck]

/assign @bowei for approval

[k8s-ci-robot]

@grayluck: GitHub didn't allow me to assign the following users: for, approval.

Note that only kubernetes members and repo collaborators can be assigned and that issues/PRs can only have 10 assignees at the same time.
For more information please see the contributor guide

In response to this:

/assign @bowei for approval

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[bowei]

/lgtm
/approve

how did this come up?

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bowei, freehan, grayluck

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Needs approval from an approver in each of these files:

• pkg/controller/nodeipam/OWNERS [bowei]

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[grayluck]

I found this issue when I am tracing how master node uses CLUTSER_IP_RANGE env and ends up here. As we removed the /24 limit in previous PR, we should also remove the validation against clusterCIDR for cloud allocator.