Tests: Replace functional tests for virt-default storage class selection with unit tests

[alromeros]

What this PR does / why we need it:

This PR removes several functional tests that verify whether the virt-default or the k8s default storage class is selected when creating a PVC/dv. These tests have historically been flaky and do not cover any functionality that cannot be tested through unit tests.

They are now replaced with equivalent unit tests.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Release note:

NONE

[coveralls]

coverage: 58.84% (+0.09%) from 58.751%
when pulling 3f52665 on alromeros:replace-virt-default-functest
into 6de420b on kubevirt:main.

[alromeros]

/retest-required

[Acedus]

Thank you @alromeros, left a couple of comments but the general transition looks great!

[Dsanatar]

/lgtm

[awels]

/approve
/hold
putting on hold to see if all the comments are addressed.

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: awels

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• OWNERS [awels]

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[arnongilboa]

/lgtm

[alromeros]

/unhold
Unholding as all the conversations have been resolved.

[Acedus]

/test pull-containerized-data-importer-e2e-nfs

[kubevirt-bot]

@alromeros: 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-containerized-data-importer-e2e-nfs	3f52665	link	true	/test pull-containerized-data-importer-e2e-nfs

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