CI: Install python dependencies

Virtualenv has been removed from the infra images, so it must be
installed manually.

Change-Id: I666dae1780303f9760f87925347accb464f30490
(cherry picked from commit 473775f147)

tests/pre.yml

@@ -12,6 +12,36 @@
         - ansible_os_family == 'Debian'
       become: true
 
+    - block:
+        # NOTE(mgoddard): The CentOS image used in CI has epel-release installed,
+        # but the configure-mirrors role used by Zuul disables epel. Since we
+        # install epel-release and expect epel to be enabled, enable it here.
+        - name: Ensure yum-utils is installed
+          package:
+            name: yum-utils
+            state: present
+
+        - name: Enable the EPEL repository
+          command: yum-config-manager --enable epel
+      become: true
+      when:
+        - ansible_os_family == "RedHat"
+
+    - name: Install Python2 modules
+      become: true
+      package:
+        name:
+          - python-pip
+          - python-setuptools
+          - python-virtualenv
+          - python-wheel
+
+    - name: Ensure latest pip is installed
+      become: true
+      pip:
+        name: pip
+        state: latest
+
     - name: Ensure /tmp/logs/ dir
       file:
         path: "{{ logs_dir }}"