Fix ElasticSearch reverse proxy settings.

* modules/logstash/templates/kibana.vhost.erb: Need to allow POST to
_aliases and _search and OPTIONS to _search. Also fix the ProxySet
settings directive by placing it in a <Proxy> section.

Change-Id: I0bb11b72eec9e8753ed8cf1d5324f411bb574f49
Merge "Fix ElasticSearch reverse proxy settings."