Add periodic cleanup of log files

When images are removed and no longer being built, their log files
hang around forever.  Add a simple cron job to clean them up after 7
days, but hide it behind a default-off flag just in case people really
want their old logs.

Change-Id: Iee55717bc5fbf88d739a4124f62f76d193cf3b75

manifests/init.pp

@@ -26,6 +26,7 @@ class nodepool (
   $statsd_host = undef,
   $vhost_name = $::fqdn,
   $image_log_document_root = '/var/log/nodepool/image',
+  $image_log_periodic_cleanup = false,
   $enable_image_log_via_http = false,
   $environment = {},
   # enable sudo for nodepool user. Useful for using dib with nodepool
@@ -303,6 +304,18 @@ class nodepool (
     }
   }
 
+  # run a cleanup on the image log directory to cleanup logs for
+  # images that are no longer being built
+  if $image_log_periodic_cleanup == true {
+    cron { 'image_log_cleanup':
+      user        => 'nodepool',
+      hour        => '1',
+      minute      => '0',
+      command     => "find ${image_log_document_root} -name '*.log' -mtime +7 -execdir rm {} \\;",
+      environment => 'PATH=/usr/bin:/bin:/usr/sbin:/sbin',
+    }
+  }
+
   if $sudo == true {
     $sudo_file_ensure = present
   }