redis should have a service check that tests for last bgsave status

[miketheman]

If a redis instance cannot complete a background save, this can affect the persistence behavior, and can lead to unexpected behaviors.

The redis info command provides rdb_last_bgsave_status - values of ok or err are what we could switch on.

https://github.com/antirez/redis/blob/4bc42ca7f6608c3e77c451c580c4b9c629480169/src/server.c#L2831

[Gourds]

I also think this is necessary