RHSM configuration is now applied conditionally only on RHEL. The same
applies to the customization to subscribe the system on first boot.
The reason is that the CentOS `@core` package group does not contain
`subscription-manager`. Thus it is not installed on CentOS Stream by
default and also CentOS 8 image definitions don't apply any changes
to the RHSM configuration [1].
In addition, make sure to not install any subscription-manager
packages on CentOS Stream images.
Regenerate all CentOS 8 image test cases.
[1] https://git.centos.org/centos/kickstarts/tree/master
Signed-off-by: Tomas Hozza <thozza@redhat.com>
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