[release-1.8] 🐛 Improve clustermodule existence check

[rikatz]

Cherry-pick of #2535 for release 1.8

[k8s-ci-robot]

@rikatz: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-vsphere-apidiff-release-1-8	0604ac0	link	false	/test pull-cluster-api-provider-vsphere-apidiff-release-1-8

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[rikatz]

/assign @sbueringer

@chrischdi @sbueringer I will try to make the cherry-pick for 1.7 tomorrow, just waiting this one to pass to make sure I didn't broke anything between releases

[sbueringer]

/lgtm

I'm fine either way regarding the public func

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: e4a4878d5d9e55282ff755a143683409e3597630

[chrischdi]

If stefans okay then I am too

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrischdi

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