[Train and before] Apply default_listen_options to ironic-inspector

93ae3c9595 introduced additional
settings to listen_options for ironic-inspector endpoint, but it didn't
merge default_listen_options but removed the default settings
completely.

This patch make sure that default settings are merged, so that some
important settings like X-Forwarded-Proto header is applied correctly.

Note that the above patch is reverted during Ussuri cycle, thus we need
this change only in Train and before.

Change-Id: I5877c07be84b8f10b4ac125ef9e22c40d2fcac0d

manifests/haproxy.pp

@@ -1370,7 +1370,8 @@ class tripleo::haproxy (
       public_ssl_port   => $ports[ironic_inspector_ssl_port],
       service_network   => $ironic_inspector_network,
       mode              => 'http',
-      listen_options    => { 'http-check' => ['expect rstring .*200.*'], },
+      listen_options    => merge($default_listen_options,
+        { 'http-check' => ['expect rstring .*200.*'], }),
     }
   }