CI: enable DNF tests on CentOS Stream 8

These were inadvertently skipped following the move to CentOS Stream,
due to matching the distro name on CentOS Linux.

Backport to Victoria.

Change-Id: I478d6304c3f8d207bc7062a0909147a169003027
(cherry picked from commit 6a69a4f)

Author: markgoddard

playbooks/kayobe-overcloud-host-configure-base/tests/test_overcloud_host_configure.py

@@ -12,7 +12,7 @@
 
 def _is_dnf():
     info = distro.linux_distribution()
-    return info[0] == 'CentOS Linux' and info[1].startswith('8')
+    return info[0].startswith('CentOS') and info[1].startswith('8')
 
 
 def test_network_ethernet(host):