Pin Ansible in rally venv

an update to ansible broke os_faults one of Rally's other deps
so we need to downgrade the version of ansible in the rally venv
for things to work.

Change-Id: Id6989b855d9b4606baf3a4fe1e5c715ab7d13543

ansible/install/roles/rally/tasks/main.yml

@@ -21,6 +21,14 @@
     version: "{{ rally_version }}"
     virtualenv: "{{ rally_venv }}"
 
+# https://github.com/openstack/rally/blob/master/requirements.txt#L6
+# remove when os-faults is fixed and rally is upgraded
+- name: Downgrade ansible in Rally venv
+  pip:
+    name: ansible
+    version: 2.3.2.0
+    virtualenv: "{{ rally_venv }}"
+
 - name: Install elasticsearch into rally-venv
   pip:
     name: elasticsearch