Mark the s390x CI as non-required

[fidencio]

Currently the s390x CI has been re-enabled but it's still not 100% stable.
Let's mark this as non-required till @BbolroC sorts out the situation.

[BbolroC]

Thanks for creating this issue @fidencio

[BbolroC]

It turns out that the failure is resolved if the backport kata-containers/tests#4633 is merged (onto kata-containers:stable-2.4).

[BbolroC]

This will be valid until the jenkins slave is migrated to IBM cloud.

[BbolroC]

The intergaration with IBM cloud has been finished. It has been showing that the CI jos for s390x gets stable since then. Even the running time becomes faster from 1h15m to 40m after kata-containers/tests#4919 and kata-containers/tests#4926 (see the results: http://jenkins.katacontainers.io/label/s390x-ubuntu-2004/). @fidencio could you include the jobs again as required and close this issue?

[BbolroC]

I have updated the relevant CI jobs for s390x at http://jenkins.katacontainers.io/view/PR%20Triggered/