feat: disable Centos 6 on s390x architecture

[nestoracunablanco]

This commit disables the generation of templates for the s390x architecture, as there are no references to CentOS 6 in the osinfo-db for this architecture.

What this PR does / why we need it: s390x enablement

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:

[openshift-ci[bot]]

Hi @nestoracunablanco. Thanks for your PR.

I'm waiting for a kubevirt member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[jcanocan]

/ok-to-test

[ksimon1]

/approve

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ksimon1

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubevirt/common-templates/blob/master/OWNERS)~~ [ksimon1] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ksimon1]

/lgtm