Update emfollow-test to Rocky Linux 8

Among RHEL and its derivatives, version 8 and later support user Systemd units. Update emfollow-test to RHEL 8 or one of its derivatives that is a candidate for the next LDAS CIT reference operating system.

In the process, we should capture a list of any special RPMs that we need in addition to the normal set of packages for LDAS CIT hosts, and include that list in the GWCelery docs.