Victoria and before: Switch syntax/unit test job to CentOS8 Stream

This is a partial backport of a75e47446a
and switches only syntax job and unit test job to CentOS8 Stream,
because these two jobs do not rely on host OS.
Integration job and litmus/beaker job on CentOS8 will be left now
but will be dropped once CentOS8 is EOLed.

Note that this change also includes the subsequent change[1] to fix
missing unit test job on CentOS8 for libraries.

[1] b54cb682d4

Conflicts:
	zuul.d/layout.yaml
	zuul.d/libraries.yaml
	zuul.d/linters.yaml
	zuul.d/unit.yaml

Change-Id: Ib7de126561d2e0a4d8cee2a596751467387eeb31
(cherry picked from commit 5ae2a889ea)
(cherry picked from commit c5504e375a)

zuul.d/layout.yaml

@@ -28,15 +28,11 @@
       jobs:
         - puppet-openstack-libraries-puppet-lint-ubuntu-bionic
         - puppet-openstack-libraries-puppet-syntax-5-centos-7
-        - puppet-openstack-libraries-puppet-syntax-5-centos-8
         - puppet-openstack-libraries-puppet-syntax-5-centos-8-stream
-        - puppet-openstack-libraries-puppet-syntax-6-centos-8
         - puppet-openstack-libraries-puppet-syntax-6-centos-8-stream
         - puppet-openstack-libraries-puppet-syntax-6-ubuntu-bionic
         - puppet-openstack-libraries-puppet-unit-5.5-centos-7
-        - puppet-openstack-libraries-puppet-unit-5.5-centos-8
         - puppet-openstack-libraries-puppet-unit-5.5-centos-8-stream
-        - puppet-openstack-libraries-puppet-unit-6.4-centos-8
         - puppet-openstack-libraries-puppet-unit-6.4-centos-8-stream
         - puppet-openstack-libraries-puppet-unit-6.4-ubuntu-bionic
         - puppet-openstack-libraries-puppet-unit-latest-ubuntu-bionic

zuul.d/libraries.yaml

@@ -8,30 +8,13 @@
     vars:
       puppet_gem_version: 5.5.0
 
-- job:
-    name: puppet-openstack-libraries-puppet-unit-5.5-centos-8
-    parent: puppet-openstack-libraries-puppet-unit-base
-    nodeset: centos-8
-    voting: false
-    vars:
-      puppet_gem_version: 5.5.0
-
 - job:
     name: puppet-openstack-libraries-puppet-unit-5.5-centos-8-stream
     parent: puppet-openstack-libraries-puppet-unit-base
     nodeset: centos-8-stream
-    voting: false
     vars:
       puppet_gem_version: 5.5.0
 
-- job:
-    name: puppet-openstack-libraries-puppet-unit-6.4-centos-8
-    parent: puppet-openstack-libraries-puppet-unit-base
-    nodeset: centos-8
-    voting: false
-    vars:
-      puppet_gem_version: 6.4.0
-
 - job:
     name: puppet-openstack-libraries-puppet-unit-6.4-centos-8-stream
     parent: puppet-openstack-libraries-puppet-unit-base

zuul.d/linters.yaml

@@ -58,13 +58,6 @@
     vars:
       puppet: 6
 
-- job:
-    name: puppet-openstack-libraries-puppet-syntax-5-centos-8
-    parent: puppet-openstack-libraries-puppet-syntax
-    nodeset: centos-8
-    vars:
-      puppet: 5
-
 - job:
     name: puppet-openstack-libraries-puppet-syntax-5-centos-8-stream
     parent: puppet-openstack-libraries-puppet-syntax
@@ -72,17 +65,9 @@
     vars:
       puppet: 5
 
-- job:
-    name: puppet-openstack-libraries-puppet-syntax-6-centos-8
-    parent: puppet-openstack-libraries-puppet-syntax
-    nodeset: centos-8
-    vars:
-      puppet: 6
-
 - job:
     name: puppet-openstack-libraries-puppet-syntax-6-centos-8-stream
     parent: puppet-openstack-libraries-puppet-syntax
     nodeset: centos-8-stream
-    voting: false
     vars:
       puppet: 6

zuul.d/unit.yaml

@@ -8,13 +8,6 @@
     vars:
       puppet_gem_version: 5.5.0
 
-- job:
-    name: puppet-openstack-unit-5.5-centos-8
-    parent: puppet-openstack-unit-base
-    nodeset: centos-8
-    vars:
-      puppet_gem_version: 5.5.0
-
 - job:
     name: puppet-openstack-unit-5.5-centos-8-stream
     parent: puppet-openstack-unit-base
@@ -22,18 +15,10 @@
     vars:
       puppet_gem_version: 5.5.0
 
-- job:
-    name: puppet-openstack-unit-6.4-centos-8
-    parent: puppet-openstack-unit-base
-    nodeset: centos-8
-    vars:
-      puppet_gem_version: 6.4.0
-
 - job:
     name: puppet-openstack-unit-6.4-centos-8-stream
     parent: puppet-openstack-unit-base
     nodeset: centos-8-stream
-    voting: false
     vars:
       puppet_gem_version: 6.4.0
 
@@ -60,9 +45,7 @@
     check:
       jobs:
         - puppet-openstack-unit-5.5-centos-7
-        - puppet-openstack-unit-5.5-centos-8
         - puppet-openstack-unit-5.5-centos-8-stream
-        - puppet-openstack-unit-6.4-centos-8
         - puppet-openstack-unit-6.4-centos-8-stream
         - puppet-openstack-unit-6.4-ubuntu-bionic
         - puppet-openstack-unit-latest-ubuntu-bionic