RHEL7 containers can no longer update on build-marist-rhel8-s390x-1

[sxa]

This is preventing regeneration of the docker images:

This system is not receiving updates. You can use subscription-manager on the host to register and assign subscriptions.

Ref: https://ci.adoptium.net/job/rhel7_docker_image_updater/label=build-marist-rhel8-s390x-1/32/console

It is likely that this is a side effect of RHEL7 on s390x going out of support earlier this year.

Related adoptium/temurin-build#3847

[sxa]

I've re-enabled the JDK10_BOOT_DIR definition on build-marist-rhel8-s390x-1 for now (set to /usr/lib/jvm/jdk-10) because this image cannot currently be updated.

Ref: #2912

(Will probably do the other variables too - the same problem may well appear for other boot JDK versions)