HAProxy Router: Add option to use PROXY protocol

Configure HAProxy to expect incoming connections on port 443 to use the
PROXY protocol if the ROUTER_USE_PROXY_PROTOCOL environment variable is set
to "true" or "TRUE".

This commit fixes bug 1385421.

https://bugzilla.redhat.com/show_bug.cgi?id=1385421

images/router/haproxy/conf/haproxy-config.template

@@ -145,7 +145,7 @@ frontend public
 # determined by the next backend in the chain which may be an app backend (passthrough termination) or a backend
 # that terminates encryption in this router (edge)
 frontend public_ssl
-  bind :{{env "ROUTER_SERVICE_HTTPS_PORT" "443"}}
+  bind :{{env "ROUTER_SERVICE_HTTPS_PORT" "443"}}{{ if matchPattern "true|TRUE" (env "ROUTER_USE_PROXY_PROTOCOL" "") }} accept-proxy{{ end }}
   tcp-request  inspect-delay 5s
   tcp-request content accept if { req_ssl_hello_type 1 }