Undercloud needs both collectd-disk and collectd-python

Unclear what has changed in OSP13, however I amd having an issue
getting collectd to start without ensuring these packages are now
installed

Change-Id: I1d7d0de1d48e0e1694db987febf9aea1c2958942

ansible/install/roles/collectd-openstack/tasks/main.yml

@@ -35,9 +35,11 @@
     - collectd
     - collectd-apache
     - collectd-ceph
+    - collectd-disk
     - collectd-mysql
-    - collectd-turbostat
     - collectd-ping
+    - collectd-python
+    - collectd-turbostat
 
 # (sai) Since we moved to containers we don't have java installed on the host
 # anymore but it is needed for collectd-java