Use puppet-openstack-module-unit-jobs to define unit test jobs

This patch replaces puppet-tripleo-module-unit-jobs by the common
job definition, puppet-openstack-module-unit-jobs, so that we run
unit test jobs which is consistent with the other puppet modules.

By merging this changes, we expect that the following change is made
to the current job definitions
- Remove CentOS7 job in master because we don't support CentOS7 anymore
- Replace puppet 6.0 job by puppet 6.14 job

Change-Id: I21d2b8f2e267a6f330cc423572b068e3910cacc4

zuul.d/layout.yaml

@@ -1,22 +1,7 @@
-- project-template:
-    name: puppet-tripleo-module-unit-jobs
-    check:
-      jobs:
-        - puppet-openstack-unit-5.5-centos-7
-        - puppet-openstack-unit-5.5-centos-8
-        - puppet-openstack-unit-6.0-ubuntu-bionic
-        - puppet-openstack-unit-latest-ubuntu-bionic:
-            voting: false
-    gate:
-      jobs:
-        - puppet-openstack-unit-5.5-centos-7
-        - puppet-openstack-unit-5.5-centos-8
-        - puppet-openstack-unit-6.0-ubuntu-bionic
-
 - project:
     templates:
       - puppet-openstack-check-jobs
-      - puppet-tripleo-module-unit-jobs
+      - puppet-openstack-module-unit-jobs
       - tripleo-undercloud-jobs
       - tripleo-multinode-container-minimal
       - release-notes-jobs-python3