Change httpchk options for horizon

In order to have clean log in apache, we need to do
a GET call instead of the default OPTIONS call. Also we
specify a User Agent, for better filtering.

Related to #237
(cherry picked from commit 98ce1341751ecd320a3701e11e6fd07cd233a5c0)

Conflicts:
	manifests/loadbalancer.pp

manifests/loadbalancer.pp

@@ -521,6 +521,7 @@ class cloud::loadbalancer(
       cloud::loadbalancer::listen_http{
         'horizon_cluster':
           ports     => $horizon_port,
+          httpchk   => "httpchk GET  /  HTTP/1.0\r\nUser-Agent:\ ${::hostname}",
           listen_ip => $vip_public_ip;
       }
     }