Downgrading Redis versions causes "Can't handle RDB version 7" errors

This occurred with two different customers today. ZenDesk: https://gitlab.zendesk.com/agent/tickets/29679

When upgrading Redis versions, the /var/opt/gitlab/redis/dump.rdb may be incompatible from one version to the other. When this happens, the following error message occurs:

2016-07-11_23:53:58.74176 [3900] 11 Jul 23:53:58.741 # Can't handle RDB format version 7
2016-07-11_23:53:58.74178 [3900] 11 Jul 23:53:58.741 # Fatal error loading the DB: Invalid argument. Exiting.

What's worse is that Redis fails to start, and the whole application doesn't boot.

The workaround right now is to remove the file and restart Redis.

Perhaps on a version change omnibus should just delete this file automatically?