Allow overriding aptly:server:secure

Change-Id: Ic660fa68eb8506a47f18d4642e7a2369948ca923
diff --git a/aptly/server/docker.yml b/aptly/server/docker.yml
index 4810e7b..b1aa4de 100644
--- a/aptly/server/docker.yml
+++ b/aptly/server/docker.yml
@@ -1,9 +1,12 @@
 classes:
   - service.aptly.server.single
 parameters:
+  _param:
+    aptly_server_secure: true
   aptly:
     server:
       enabled: true
+      secure: ${_param:aptly_server_secure}
       source:
         engine: docker
         image: tcpcloud/aptly