Fix scope of vhost template variable

Dynamic scoping for variables in ERB templates was removed in puppet
4[1], so look up the @serveradmin variable from the scope object.

[1] https://puppet.com/docs/puppet/4.10/lang_updating_manifests.html#dynamic-scoping-in-erb

Change-Id: Ia53125bed102193e149f995430bbdf10dfdbf428

templates/hound.vhost.erb

@@ -5,7 +5,7 @@
 <% elsif @serveraliases -%>
 <%= "  ServerAlias #{@serveraliases}" %>
 <% end %>
-  ServerAdmin <%= @serveradmin %>
+  ServerAdmin <%= scope.lookupvar("hound::serveradmin") %>
 
   ErrorLog ${APACHE_LOG_DIR}/<%= scope.lookupvar("hound::vhost_name") %>-error.log