ensure the redis connection stays shared on reconnect
ensure the redis connection stays shared on reconnect

test plan:
 * configure redis.yml
 * configure cache_store.yml for development/production to be
   cache_store: redis_store and nothing else
 * open console
 * Canvas.redis.__getobj__.object_id should be the same as
   Rails.cache.instance_variable_get(:@data).object_id
 * Run Canvas.reconnect_redis and they should still be the same
 * netstat -an should show only one connection from your console
   process to the redis server

Change-Id: I534eb8b522cc56e6b21bc271d610940b59118f50
Reviewed-on: https://gerrit.instructure.com/93864
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Tested-by: Jenkins
QA-Review: Benjamin Christian Nelson <4a283f6b032925e40a485c88ede5597d7d65a090@instructure.com>
Product-Review: Brian Palmer <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@instructure.com>

sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,SwinburneOnline/canvas-lms,matematikk-mooc/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,venturehive/canvas-lms,matematikk-mooc/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms