Ensure we use paho 1.2.3

The new paho-mqtt 1.3.0 release brings
https://github.com/eclipse/paho.mqtt.python/commit/0a8cccc
which prevents its use on Ubuntu Trusty's default Python interpreter.
Until we upgrade to a newer Python there, stay on paho-mqtt 1.2.3 so
that things keep working.

Change-Id: I4ffcd8c7906c86a40f3cd8f8d83fb8208944d189

manifests/init.pp

@@ -76,9 +76,11 @@ class log_processor (
     provider => openstack_pip,
     require  => Class['pip'],
   }
+  # Temporarily pin paho-mqtt to 1.2.3 since 1.3.0 won't support TLS on
+  # Trusty's Python 2.7.
   if ! defined(Package['paho-mqtt']) {
     package { 'paho-mqtt':
-      ensure   => latest,
+      ensure   => '1.2.3',
       provider => openstack_pip,
       require  => Class['pip'],
     }