caddy-frontend: Always fill-in key download url

Kedifa requires some time to process new slave, and during that time the key
download URL is not available, but as it is required for proper mapping file,
use some url to mimic it.

software/caddy-frontend/buildout.hash.cfg

@@ -30,7 +30,7 @@ md5sum = d62aefe002ec13875924e4c219914795
 
 [template-slave-list]
 filename = templates/apache-custom-slave-list.cfg.in
-md5sum = e0d0c9fc7d4bf95dac580bbc1d2a4d93
+md5sum = be47649fba6b44e136c3a8eb538443f3
 
 [template-slave-configuration]
 filename = templates/custom-virtualhost.conf.in

software/caddy-frontend/templates/apache-custom-slave-list.cfg.in

@@ -32,6 +32,8 @@ create = true
 
 {% if master_key_download_url %}
 {%   do kedifa_updater_mapping.append((master_key_download_url, master_certificate, apache_certificate)) %}
+{% else %}
+{%   do kedifa_updater_mapping.append(('https://notreadyyet', master_certificate, apache_certificate)) %}
 {% endif %}
 
 {% if slave_kedifa_information %}
@@ -55,7 +57,7 @@ output = {{ plugin_directory }}/${:name}
 {%   if slave_kedifa %}
 {%     set key_download_url = slave_kedifa.get('key-download-url') %}
 {%   else %}
-{%     set key_download_url = '' %}
+{%     set key_download_url = 'http://notreadyyet' %}
 {%   endif %}
 {%   set slave_type = slave_instance.get('type', '') %}
 {%   set slave_section_title = 'dynamic-template-slave-instance-%s' % slave_reference %}