fix negative caching of scribd mime types
fix negative caching of scribd mime types

refs CNVS-6947

test plan:
 * download a zip of multiple different folders from the UI
 * check the log of the ContentZipper jobs; there should only be
   one query in the first job querying scribd_mime_types for
   "unknown/unknown"

Change-Id: I8ade4f783c124ff6324e5dad8fdd0574aaf58d58
Reviewed-on: https://gerrit.instructure.com/22411
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Jacob Fugal <f862f167b85d41b225785c70d70808bc7337c1fe@instructure.com>
QA-Review: Jeremy Putnam <b030d6d6f199f844ec424882be473c2ab9adc93b@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

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