Adds podman-package-centos-7 job

As reviewer pointed on below comment, we may need to test with an
older system to validate rpm building.

Change-Id: Ie1b16db032e79eeb7ba9a674455ffa9023bae63d
Needed-By: containers/podman#4795

playbooks/podman/pre.yaml

@@ -13,6 +13,22 @@
         dnf repolist
       changed_when: true
 
+    - name: Enable EPEL for Centos-7
+      when:
+        - ansible_distribution_major_version == "7"
+        - ansible_distribution == "CentOS"
+      block:
+
+        - name: Enable EPEL
+          become: true
+          package:
+            name: epel-release
+
+        # CI images may have epel-release pre-installed but disabled!
+        - name: Enable EPEL
+          become: true
+          command: yum-config-manager --enable epel
+
     - name: Install pre-requisites
       become: true
       package:

zuul.d/podman.yaml

@@ -21,6 +21,14 @@
       - name: opendev.org/openstack/tripleo-heat-templates
       - name: github.com/containers/libpod
 
+- job:
+    name: podman-package-centos-7
+    parent: podman-package-centos-8
+    nodeset:
+      nodes:
+        - name: test
+          label: upstream-centos-7
+
 - job:
     name: podman-package-rhel-8
     parent: podman-package-centos-8

zuul.d/projects.yaml

@@ -53,6 +53,7 @@
               - playbooks/podman/.*
             # until we fix https://github.com/containers/libpod/issues/4665
             voting: false
+        - podman-package-centos-7: *podman
         - podman-package-centos-8: *podman
         - podman-package-fedora-30: *podman