Temporarily disable intermediate registry prune

Just to eliminate the possibility that a bug in this may be causing
us to erroneously delete blobs.

Change-Id: I048d9ae5ba92984c90f84f231b412050a52fcea6

playbooks/roles/registry/tasks/main.yaml

@@ -42,9 +42,11 @@
 - name: Run docker prune to cleanup unneeded images
   shell:
     cmd: docker image prune -f
-- name: Install cron to garbage collect the registry daily
-  cron:
-    name: "docker registry garbage-collect"
-    minute: "0"
-    hour: "0"
-    job: "/usr/bin/docker exec registrydocker_registry_1 zuul-registry prune"
+# Temporarily disable to aid debug of mysteriously absent blobs
+# -corvus 2019-10-09
+# - name: Install cron to garbage collect the registry daily
+#   cron:
+#     name: "docker registry garbage-collect"
+#     minute: "0"
+#     hour: "0"
+#     job: "/usr/bin/docker exec registrydocker_registry_1 zuul-registry prune"