allow fetching all existing values for a MultiCache
allow fetching all existing values for a MultiCache

just use fetch(key, node: :all) without a block

Change-Id: I9015b5db56991aebe599f143f4ea4d97beeb40b5
Reviewed-on: https://gerrit.instructure.com/90080
Tested-by: Jenkins
Reviewed-by: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

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