Use full lookup path for serveradmin in template

The last change was incomplete bceause we evaluate the apache conf
template in the context of the httpd class meaning any vars outside of
that class must be fully qualified lookups. Make serveradmin a fully
qualified lookup.

Change-Id: I709af6a78316cd1ca7e489d62f13e988997f3157

templates/dual-elasticsearch.vhost.erb

@@ -1,6 +1,6 @@
 <VirtualHost *:80>
   ServerName <%= @vhost_name %>
-  ServerAdmin <%= @serveradmin %>
+  ServerAdmin <%= scope.lookupvar('::kibana::js::serveradmin') %>
 <% if @serveraliases.is_a? Array %>
 <% @serveraliases.each do |name| %><%= "  ServerAlias #{name}\n" %><% end %>
 <% elsif ! ['', nil].include?(@serveraliases) %>