fix RHUI support for RHEL 7 clients

[mcalmer]

What does this PR change?

Fix RHUI support for RHEL 7 client. As 8 and 9 may see the same in future, applied the same change also to the other script.
RedHat changed the hostnames of the RHUI repository server to include numbers in the name.

rhui.x.y.z => rhui3.x.y.z

Links

Port of https://github.com/SUSE/spacewalk/pull/22598

• DONE

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