Fix an issue with redis keys not hitting

[joegaudet]

When writing to a redis store, the keys used by JR are converted to
slash delimited strings. So:

key = [record_type, id, updated at]

Gets converted to record_type/id/updated_at

This causes the lookup function to never get hits from the redis store.

This commit adds a configurable function to allow formating of the
lookup key.

[DavidMikeSimon]

@joegaudet This particular issue with redis has been reported before in #917, and I wasn't able to reproduce it. Can you tell me more about your environment, e.g. Ruby version, name and version of redis gem used?

[joegaudet]

@DavidMikeSimon Gems:

gem 'redis-rails', '> 4.0.0' # Rails Redis adapters, caching, sessions, etc.
gem 'redis-namespace', '> 1.5.0' # namespacing for Redis
gem 'rails', '~> 4.2.0'

ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]

So the issue seems to be in the way things get written to redis, our keys looks like this:

orders/321/2017-04-26 23:52:58 UTC/SRLZ-sZHh1BNSdDAaht97RdKB23JJ8+D5bQpy28pQdI5xFhg=/ATTR-CTX-k_+raGkUaGivBBbrqmIyPlG3wldRXXdUeNbg1_d37K0=

record-type/record-id/updated-at/hash

Where the JR system appears to use an array as the key.