change tripleo centos-7 build containers to centos-8

mark the job non-voting
remove the gate job.

Once the job is confirmed stable we should
add voting, gating.

Change-Id: Ied6df5412c58446c6b090bc8e9822685ed51ddb1

.zuul.d/centos.yaml

@@ -11,8 +11,8 @@
         - kolla-ansible-centos-binary
         - kolla-ansible-centos8-binary
         - kolla-ansible-centos-source-upgrade
-        - tripleo-build-containers-centos-7:
+        - tripleo-build-containers-centos-8:
-            voting: true
+            voting: false
             files:
               - ^.zuul.d/centos.yaml$
               - ^docker/.*$
@@ -50,15 +50,6 @@
         - kolla-ansible-centos-source
         - kolla-ansible-centos8-source
         - kolla-ansible-centos-source-upgrade
-        - tripleo-build-containers-centos-7:
-            voting: true
-            files:
-              - ^.zuul.d/centos.yaml$
-              - ^docker/.*$
-              - ^kolla/.*$
-              - ^requirements.txt$
-              - ^setup.cfg$
-              - ^setup.py$
     periodic:
       jobs:
         - kolla-publish-centos-source