Run nodepool cleanup every 5 mins

It's early days; if nodepool barfs and we have to munge the db or
restart it, this will clean up not-quite-deleted nodes faster.

Change-Id: I854378966150aaeffed6de223de5e04daa83112a

modules/openstack_project/templates/nodepool/nodepool.yaml.erb

@@ -2,7 +2,7 @@ script-dir: /etc/nodepool/scripts
 dburi: 'mysql://nodepool:<%= mysql_password %>@localhost/nodepool'
 
 cron:
-  cleanup: '27 */6 * * *'
+  cleanup: '*/5 * * * *'
   update-image: '14 2 * * *'
 
 zmq-publishers: