The packaging of fetch-crl in EPEL-8 uses a systemd timer unit,
instead of a cron job, to run fetch-crl regularly.  Thus, in EL-8
we need to manage the 'fetch-crl.timer' service instead of the old
'fetch-crl-cron' and 'fetch-crl-boot' services.

Signed-off-by: Thomas Bellman <bellman@nsc.liu.se>