slaprunner: no more need of hardcoded path for monitoring url

software/slaprunner/instance-runner.cfg

@@ -416,7 +416,7 @@ access_url = $${:url}/login
 url =  https://$${request-frontend:connection-domain}
 ssh_command = ssh $${dropbear-runner-server:host} -p $${dropbear-runner-server:port}
 webdav_url = https://$${request-frontend:connection-domain}/share
-monitor_url = https://$${monitor-frontend:connection-domain}/index.cgi
+monitor_url = https://$${monitor-frontend:connection-domain}
 public_url =  $${:url}/public/
 
 #---------------------------