Fix infra secret lookup so that it defaults to the namespace of the referencing resource

[pjaton]

What this PR does / why we need it:

This change fixes where the GenerateInfraClusterClient function looks up for the infrastructure secret referenced in a KubevirtCluster or KubevirtMachine, when no namespace is specified in the ObjectReference.

This corrects the current logic by ensuring that, in this case, the code looks for the secret in the same namespace than the referencing resource; which aligns with the default behavior that CAPI follows for other ObjectReferences.

To validate this change of behavior, this PR also introduce a set of tests for the infracluster package.

Which issue this PR fixes:

fixes #165

Special notes for your reviewer:

Note that this change is split in two commits:

• The first one with a refactoring that extract the duplicated setupScheme() function into as single function in the testing package.
• The second commit introduces the fix and the tests validating the infracluster package.

Release notes:

NONE

[coveralls]

Pull Request Test Coverage Report for Build 2775158040

• 14 of 14 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.1%) to 49.486%

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Totals
Change from base Build 2763291491:	1.1%
Covered Lines:	819
Relevant Lines:	1655

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💛 - Coveralls

[davidvossel]

/ok-to-test

[davidvossel]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: davidvossel, pjaton

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• OWNERS [davidvossel]

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[agradouski]

/lgtm