Log Message:
databases/redis: Update to 4.0.9.

- Fix a critical AOF bug when fsync policy set to "always"
- Latency monitor could report wrong latencies under certain conditions.
- AOF rewriting could fail when a backgronud rewrite is triggered and
  at the same time the AOF is switched on/off.
- Redis Cluster crash-recovery safety improved.
- Other smaller fixes (check commnits).
- Redis Cluster has now the ability to configure certain slaves so that
  they'll never attempt a failover.
- Keyspace notifications API in modules.
- RM_Call() is now faster by reusing the same client.
- Tracking of the percentage of keys already logically expired but yet
  not evicted.