add oplog to backup for consistent restores, move away from gzip to enable better deduplication

tasks/backup.yml

@@ -17,6 +17,6 @@
 - name: add backup cleanup cronjob
   cron:
     name: mongodb backup cleanup
-    job: 'find /opt/mongodbbackup/ -mtime +{{ mongodb.backup.keep_days - 1 }} -type d -mindepth 1 -exec rm -r {} \;'
+    job: 'find /opt/mongodbbackup/ -mindepth 1 -maxdepth 1 -mtime +{{ mongodb.backup.keep_days - 1 }} -type d -exec rm -r {} \;'
     minute: "0"
     hour: "5"