Pobrien/issue 408

Persistence should crash on generating an error

/cc @zendesk/zendesk-radar

### Steps to merge
 - [ ] :+1: of the team


### References
 - Jira link: https://zendesk.atlassian.net/browse/RADAR-408

### Risks
 - Low: Connection to redis/sentinel does not failover. 
I am not sure of the whole range of errors that can be returned from redis. (Specifically things like setnx etc) It's probably better to figure out the errors we want to hard-crash on and only crash for them. For example: Write to slave error.