feat: disable Centos 7 on s390x architecture

[nestoracunablanco]

This commit disables the generation of templates for the s390x architecture, as there are no references to CentOS 7 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:

NONE

[kubevirt-bot]

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[openshift-ci]

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.

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[ksimon1]

@nestoracunablanco FYI #621

[nestoracunablanco]

@ksimon1, thank you for the information. I will keep this PR on hold until #621 is approved or merged.

[nestoracunablanco]

/hold