Fix default mode in haproxy_single_service_split

haproxy_single_service_listen (the default template) was already fine.

Closes-Bug: #1896591
TrivialFix

Change-Id: Id68fe19ea87565aa36fb74f2a2ca66cb951169f6

ansible/roles/haproxy-config/templates/haproxy_single_service_split.cfg.j2

@@ -128,7 +128,7 @@ backend {{ service_name }}_back
 {{ frontend_macro(haproxy_name, haproxy_service.port, mode, external,
                   frontend_http_extra, frontend_tcp_extra) }}
         {# Redirect (to https) is a special case, as it does not include a backend #}
-        {% if haproxy_service.mode != 'redirect' %}
+        {% if mode != 'redirect' %}
 {{ backend_macro(haproxy_name, listen_port, mode, host_group,
                  custom_member_list, backend_http_extra, backend_tcp_extra,
                  auth_user, auth_pass, tls_backend) }}

releasenotes/notes/bug-1896591-47c829f8b72d567a.yaml

+---
+fixes:
+  - |
+    Fixes ``haproxy_single_service_split`` template to work with default for
+    ``mode`` (``http``).
+    `LP#1896591 <https://launchpad.net/bugs/1896591>`__