don't cache discussion topic html to work with marking as read
don't cache discussion topic html to work with marking as read

Change-Id: I116059708a3271c6dce786d7286b85bc24cc536f
fixes: #7724
Reviewed-on: https://gerrit.instructure.com/9430
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>
Reviewed-by: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>

parbros/red-innovadores-lms,loganrun/pincan,sfu/canvas-lms,Unow/ins,fronteerio/canvas-lms,skmezanul/canvas-lms,HotChalk/canvas-lms,shidao-fm/canvas-lms,efrj/canvas-lms,jay3126/canvas-lms,jay3126/canvas-lms,venturehive/canvas-lms,ShreniiNepal/shrenii_lmp,fronteerio/canvas-lms,ankithbti/canvas_lms,jay3126/canvas-lms,ankithbti/canvas_lms,venturehive/canvas-lms,djbender/canvas-lms,greyhwndz/canvas-lms,rup/Tarrax,SwinburneOnline/canvas-lms,sdeleon28/canvas-lms,rup/Tarrax,tgroshon/canvas-lms,samuels410/greatlakes-lms,grahamb/canvas-lms,utkarshx/canvas-lms,leftplusrightllc/canvas-lms,sfu/canvas-lms,arrivu/arrivu-lms,merichar/canvas-lms,grahamb/canvas-lms,utkarshx/canvas-lms,antoniuslin/canvas-lms,wimemx/Canvas,fronteerio/canvas-lms,ShreniiNepal/shrenii_lmp,juoni/canvas-lms,kyroskoh/canvas-lms,whalejasmine/canvas-lms,arrivu/hoodemo,nditech/red-innovadores-lms,sdeleon28/canvas-lms,Unow/ins,ShreniiNepal/shrenii_lmp,juoni/canvas-lms,wye0220/shindig-canvas,arrivu/jigsaw-lms,Rvor/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,sli7246/canvas_branch,antoniuslin/canvas-lms,Rvor/canvas-lms,usmschuck/canvas,rup/Tarrax,loganrun/pincan,arrivu/qibla-ecampus,tgroshon/canvas-lms,parbros/red-innovadores-lms,wrdsb/canvas-lms,redconfetti/canvas-lms,grahamb/canvas-lms,nditech/red-innovadores-lms,nditech/red-innovadores-lms,arrivu/jigsaw-lms,landonwilkins/canvas-lms,loganrun/pincan,djbender/canvas-lms,utkarshx/canvas-lms,Rvor/canvas-lms,wrdsb/canvas-lms,arrivu/arrivu-lms,tgroshon/canvas-lms,grahamb/canvas-lms,landonwilkins/canvas-lms,leftplusrightllc/canvas-lms,shidao-fm/canvas-lms,sli7246/canvas_branch,parbros/red-innovadores-lms,va7map/canvas-lms,whalejasmine/canvas-lms,venturehive/canvas-lms,efrj/canvas-lms,kyroskoh/canvas-lms,Jyaasa/canvas-lms,landonwilkins/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,sdeleon28/canvas-lms,wimemx/Canvas,venturehive/canvas-lms,landonwilkins/canvas-lms,kyroskoh/canvas-lms,samuels410/greatlakes-lms,Unow/ins,nditech/red-innovadores-lms,samuels410/greatlakes-lms,ankithbti/canvas_lms,wimemx/Canvas,djbender/canvas-lms,efrj/canvas-lms,Jyaasa/canvas-lms,antoniuslin/canvas-lms,whalejasmine/canvas-lms,merichar/canvas-lms,wye0220/shindig-canvas,djbender/canvas-lms,whalejasmine/canvas-lms,sfu/canvas-lms,em2/canvas-lms,HotChalk/canvas-lms,juoni/canvas-lms,sfu/canvas-lms,utkarshx/canvas-lms,SwinburneOnline/canvas-lms,wrdsb/canvas-lms,kyroskoh/canvas-lms,fronteerio/canvas-lms,wrdsb/canvas-lms,sdeleon28/canvas-lms,arrivu/qibla-ecampus,roxolan/canvas-lms,sfu/canvas-lms,arrivu/arrivu-lms,skmezanul/canvas-lms,va7map/canvas-lms,redconfetti/canvas-lms,jay3126/canvas-lms,grahamb/canvas-lms,usmschuck/canvas,tgroshon/canvas-lms,va7map/canvas-lms,leftplusrightllc/canvas-lms,skmezanul/canvas-lms,redconfetti/canvas-lms,Jyaasa/canvas-lms,efrj/canvas-lms,shidao-fm/canvas-lms,sfu/canvas-lms,em2/canvas-lms,greyhwndz/canvas-lms,Rvor/canvas-lms,arrivu/jigsaw-lms,arrivu/hoodemo,Unow/canvas-lms,wye0220/shindig-canvas,SwinburneOnline/canvas-lms,roxolan/canvas-lms,arrivu/hoodemo,greyhwndz/canvas-lms,shidao-fm/canvas-lms,Jyaasa/canvas-lms,roxolan/canvas-lms,merichar/canvas-lms,HotChalk/canvas-lms,usmschuck/canvas,leftplusrightllc/canvas-lms,em2/canvas-lms,greyhwndz/canvas-lms,redconfetti/canvas-lms,antoniuslin/canvas-lms,skmezanul/canvas-lms,SwinburneOnline/canvas-lms,Unow/canvas-lms,arrivu/qibla-ecampus,Unow/canvas-lms,ShreniiNepal/shrenii_lmp,samuels410/greatlakes-lms,usmschuck/canvas,sli7246/canvas_branch,va7map/canvas-lms