gracefully handle absence of cache_store.yml
gracefully handle absence of cache_store.yml

test-plan:

 - don't have a config/cache_store.yml
 - try and boot canvas

Change-Id: I58ceca7bc3b618421e7d66987bbd18b2646babf4
Reviewed-on: https://gerrit.instructure.com/29582
QA-Review: Jeremy Putnam <b030d6d6f199f844ec424882be473c2ab9adc93b@instructure.com>
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Product-Review: Jacob Fugal <f862f167b85d41b225785c70d70808bc7337c1fe@instructure.com>

samuels410/greatlakes-lms,Unow/canvas-lms,leftplusrightllc/canvas-lms,gbleydon/canvas-lms,antoniuslin/canvas-lms,wrdsb/canvas-lms,ShreniiNepal/shrenii_lmp,grahamb/canvas-lms,roxolan/canvas-lms,juoni/canvas-lms,Jyaasa/canvas-lms,venturehive/canvas-lms,Jyaasa/canvas-lms,samuels410/greatlakes-lms,sfu/canvas-lms,samuels410/greatlakes-lms,grahamb/canvas-lms,kyroskoh/canvas-lms,skmezanul/canvas-lms,usmschuck/canvas,grahamb/canvas-lms,fronteerio/canvas-lms,matematikk-mooc/canvas-lms,jay3126/canvas-lms,wrdsb/canvas-lms,roxolan/canvas-lms,eCNAP/CANVAS,tgroshon/canvas-lms,utkarshx/canvas-lms,tgroshon/canvas-lms,djbender/canvas-lms,leftplusrightllc/canvas-lms,wrdsb/canvas-lms,juoni/canvas-lms,narigone/canvas,shidao-fm/canvas-lms,snehakachroo1/LSI_replica,arrivu/arrivu-lms,sfu/canvas-lms,va7map/canvas-lms,SwinburneOnline/canvas-lms,arrivu/arrivu-lms,snehakachroo1/LSI_replica,Rvor/canvas-lms,instructure/canvas-lms,kyroskoh/canvas-lms,dgynn/canvas-lms,arrivu/arrivu-lms,greyhwndz/canvas-lms,instructure/canvas-lms,efrj/canvas-lms,va7map/canvas-lms,redconfetti/canvas-lms,narigone/canvas,snehakachroo1/LSI_replica,kyroskoh/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,va7map/canvas-lms,wye0220/shindig-canvas,samuels410/greatlakes-lms,Jyaasa/canvas-lms,dgynn/canvas-lms,matematikk-mooc/canvas-lms,usmschuck/canvas,Rvor/canvas-lms,sfu/canvas-lms,eCNAP/CANVAS,greyhwndz/canvas-lms,Rvor/canvas-lms,efrj/canvas-lms,redconfetti/canvas-lms,redconfetti/canvas-lms,Jyaasa/canvas-lms,venturehive/canvas-lms,fronteerio/canvas-lms,wrdsb/canvas-lms,shidao-fm/canvas-lms,instructure/canvas-lms,gbleydon/canvas-lms,AndranikMarkosyan/lms,roxolan/canvas-lms,HotChalk/canvas-lms,gbleydon/canvas-lms,efrj/canvas-lms,efrj/canvas-lms,djbender/canvas-lms,arrivu/hoodemo,venturehive/canvas-lms,AndranikMarkosyan/lms,narigone/canvas,sdeleon28/canvas-lms,utkarshx/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,shidao-fm/canvas-lms,utkarshx/canvas-lms,utkarshx/canvas-lms,sdeleon28/canvas-lms,instructure/canvas-lms,jay3126/canvas-lms,arrivu/hoodemo,antoniuslin/canvas-lms,antoniuslin/canvas-lms,shidao-fm/canvas-lms,HotChalk/canvas-lms,matematikk-mooc/canvas-lms,va7map/canvas-lms,jay3126/canvas-lms,Unow/canvas-lms,sfu/canvas-lms,AndranikMarkosyan/lms,juoni/canvas-lms,matematikk-mooc/canvas-lms,eCNAP/CANVAS,tgroshon/canvas-lms,jay3126/canvas-lms,sfu/canvas-lms,roxolan/canvas-lms,leftplusrightllc/canvas-lms,antoniuslin/canvas-lms,fronteerio/canvas-lms,skmezanul/canvas-lms,ShreniiNepal/shrenii_lmp,ShreniiNepal/shrenii_lmp,sdeleon28/canvas-lms,tgroshon/canvas-lms,narigone/canvas,SwinburneOnline/canvas-lms,arrivu/hoodemo,wye0220/shindig-canvas,sfu/canvas-lms,djbender/canvas-lms,skmezanul/canvas-lms,dgynn/canvas-lms,SwinburneOnline/canvas-lms,whalejasmine/canvas-lms,redconfetti/canvas-lms,Rvor/canvas-lms,AndranikMarkosyan/lms,greyhwndz/canvas-lms,usmschuck/canvas,grahamb/canvas-lms,greyhwndz/canvas-lms,usmschuck/canvas,dgynn/canvas-lms,instructure/canvas-lms,kyroskoh/canvas-lms,grahamb/canvas-lms,leftplusrightllc/canvas-lms,sdeleon28/canvas-lms,venturehive/canvas-lms,HotChalk/canvas-lms,whalejasmine/canvas-lms,djbender/canvas-lms,wye0220/shindig-canvas,skmezanul/canvas-lms,whalejasmine/canvas-lms,fronteerio/canvas-lms,snehakachroo1/LSI_replica,ShreniiNepal/shrenii_lmp,instructure/canvas-lms,Unow/canvas-lms,juoni/canvas-lms,whalejasmine/canvas-lms,eCNAP/CANVAS