Add sixth elasticsearch node.

* manifests/site.pp: Put elasticsearch nodes in a list variable that is
reused.

* modules/logstash/templates/elasticsearch.yml.erb: Update cluster
settings to be more appropriate for the larger cluster size, including
changing the minimum number of master eligible nodes that must be seen
before becoming operational in a cluster. Should help prevent split
brained clusters.

* modules/openstack_project/manifests/cacti.pp: Add new node to cacti
node list.

Change-Id: I9a18422aa56a56b9ad030892a312772d9b6b2a79
Merge "Add sixth elasticsearch node."