Re-enable CentOS 8 in CI

5 jobs for rpm_selinux in 35 minutes and 14 seconds (queued for 24 seconds)
latest
Status Job ID Name Coverage
  Build
passed #44802
build_bionic

00:11:45

passed #44801
build_buster

00:10:13

passed #44803
build_centos_7

00:14:34

passed #44804
build_centos_8

00:10:01

passed #44800
build_stretch

00:13:32