Docker garbage collection

Remove all stopped containers, networks not used
by at least one container, dangling images,
build cache >= 1 week.

Change-Id: I1cd93ac35fa6caca5b0c4b5781311459e58aac9a
Closes-bug: PROD-21595
diff --git a/docker/host.yml b/docker/host.yml
index aef7a32..bb3dffa 100644
--- a/docker/host.yml
+++ b/docker/host.yml
@@ -1,6 +1,8 @@
 classes:
   - service.docker.host
 parameters:
+  _param:
+    docker_garbage_collection_enabled: false
   docker:
     host:
       pkgs:
@@ -14,3 +16,16 @@
         ipv6: true
         fixed-cidr-v6: fc00::/7
         storage-driver: overlay2
+  linux:
+    system:
+      cron:
+        user:
+          root:
+            enabled: true
+      job:
+        docker_garbage_collection:
+          command: docker system prune -f --filter until=$(date +%s -d "1 week ago")
+          enabled: ${_param:docker_garbage_collection_enabled}
+          user: root
+          hour: 6
+          minute: 0