Include package python-dateutils

A script that runs when an asset is added to the app catalog
relies on python-dateutils. When it is not available, it
fails silently, and does not update the date that asset was
last modified. This commit will include that package.

Change-Id: I43b42c8e9d2a6053f9817c63bdc65c5b35eec485
Closes-Bug: 1553572

manifests/init.pp

@@ -92,6 +92,12 @@ class apps_site (
     }
   }
 
+  if ! defined(Package['python-dateutil']) {
+    package { 'python-dateutil':
+      ensure => present,
+    }
+  }
+
   if ($::lsbdistcodename == 'trusty') {
     if ! defined(Package['zopfli']) {
       package { 'zopfli':