Allow disabling proxy_http_version directive

The EPEL 6 repository still has version 1.0.15 which does not support
this directive proxy_http_version. Yes, this version is old, but a lot
of people prefer not to use a bleeding edge version from nginx.org.

manifests/config.pp

@@ -106,7 +106,9 @@
   }
   validate_string($multi_accept)
   validate_array($proxy_set_header)
-  validate_string($proxy_http_version)
+  if ($proxy_http_version != false) {
+    validate_string($proxy_http_version)
+  }
   validate_bool($confd_purge)
   validate_bool($vhost_purge)
   if ($proxy_cache_path != false) {

templates/conf.d/proxy.conf.erb

@@ -8,7 +8,8 @@ proxy_send_timeout      <%= @proxy_send_timeout %>;
 proxy_read_timeout      <%= @proxy_read_timeout %>;
 proxy_buffers           <%= @proxy_buffers %>;
 proxy_buffer_size       <%= @proxy_buffer_size %>;
-proxy_http_version      <%= @proxy_http_version %>;
+<% if @proxy_http_version -%>
+proxy_http_version      <%= @proxy_http_version %>;<% end %>
 <% @proxy_set_header.each do |header| %>
 proxy_set_header        <%= header %>;<% end %>
 proxy_headers_hash_bucket_size <%= @proxy_headers_hash_bucket_size %>;