Use CentOS8 to run unit tests and lint tests

This patch makes CentOS8 jobs voting and CentOS7 jobs disabled for
unit tests and lint tests, so that we use CentOS8 for default CentOS
to run jobs for current master.

Change-Id: Ic6abf9f09bb687e830a06e7129f77e2504ea8e2a

zuul.d/linters.yaml

@@ -65,6 +65,7 @@
     name: puppet-openstack-libraries-puppet-syntax-5-centos-7
     parent: puppet-openstack-libraries-puppet-syntax
     nodeset: centos-7
+    branches: ^stable/(ocata|pike|queens|rocky|stein|train)$
     vars:
       puppet: 5
 
@@ -79,7 +80,6 @@
     name: puppet-openstack-libraries-puppet-syntax-5-centos-8
     parent: puppet-openstack-libraries-puppet-syntax
     nodeset: centos-8
-    voting: false
     branches: ^(?!stable/(ocata|pike|queens|rocky|stein)).*$
     vars:
       puppet: 5
@@ -88,7 +88,6 @@
     name: puppet-openstack-libraries-puppet-syntax-6-centos-8
     parent: puppet-openstack-libraries-puppet-syntax
     nodeset: centos-8
-    voting: false
     branches: ^(?!stable/(ocata|pike|queens|rocky|stein)).*$
     vars:
       puppet: 6

zuul.d/unit.yaml

@@ -12,6 +12,7 @@
 - job:
     name: puppet-openstack-unit-5.5-centos-7
     parent: puppet-openstack-unit-base
+    branches: ^stable/(ocata|pike|queens|rocky|stein|train)$
     nodeset: centos-7
     vars:
       puppet_gem_version: 5.5
@@ -20,7 +21,6 @@
     name: puppet-openstack-unit-5.5-centos-8
     parent: puppet-openstack-unit-base
     nodeset: centos-8
-    voting: false
     branches: ^(?!stable/(ocata|pike|queens|rocky|stein)).*$
     vars:
       puppet_gem_version: 5.5
@@ -29,7 +29,6 @@
     name: puppet-openstack-unit-6.11-centos-8
     parent: puppet-openstack-unit-base
     nodeset: centos-8
-    voting: false
     branches: ^(?!stable/(ocata|pike|queens|rocky|stein)).*$
     vars:
       puppet_gem_version: 6.11