Fix default cleanup command

This patch ensures that the default cleanup command will not try to
delete the backup directory itself. It will now, however, delete files
recursively, removing old directories, even if they contain newer
contents.

defaults/main.yml

@@ -24,5 +24,8 @@ backup_group: "{{ backup_user }}"
 #   FILENAME="{{ backup_mountpoint }}/$(date '+%Y%m%d-%H%M%S').sql.gz"
 #   mysqldump -u root --no-data dbname | gzip > "${FILENAME}"
 
-backup_cleanup: |
-  find "{{ backup_mountpoint }}" -mtime "+{{ backup_keep_days }}" -delete
+backup_cleanup: >-
+  find "{{ backup_mountpoint }}"
+  -mindepth 2
+  -mtime "+{{ backup_keep_days }}"
+  -exec rm -rfv '{}' \;