chore: pin ingress-nginx to the control plane to fix #657 (#664)

diff --git a/roles/ingress_nginx/vars/main.yml b/roles/ingress_nginx/vars/main.yml
index f62eb4e..6480bc2 100644
--- a/roles/ingress_nginx/vars/main.yml
+++ b/roles/ingress_nginx/vars/main.yml
@@ -42,6 +42,8 @@
     metrics:
       enabled: true
   defaultBackend:
+    nodeSelector:
+      openstack-control-plane: enabled
     enabled: true
     image:
       registry: "{{ atmosphere_images['ingress_nginx_default_backend'] | vexxhost.kubernetes.docker_image('domain') }}"