avoid trying to create a wiki in Course#tabs_available
avoid trying to create a wiki in Course#tabs_available

test plan:
 * with a read-only slave environment
 * create a new course
 * go to the course
 * it should not error

Change-Id: Ie0003cec2b684fca1400e6efbcca434a540d5c7a
Reviewed-on: https://gerrit.instructure.com/13032
Reviewed-by: Zach Wily <9de8c4480303b5335cd2a33eefe814615ba3612a@instructure.com>
Tested-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

icelab/canvas,greyhwndz/canvas-lms,rup/Tarrax,nditech/red-innovadores-lms,fronteerio/canvas-lms,whalejasmine/canvas-lms,redconfetti/canvas-lms,dgynn/canvas-lms,narigone/canvas,leftplusrightllc/canvas-lms,antoniuslin/canvas-lms,arrivu/hiring-site,samuels410/greatlakes-lms,roxolan/canvas-lms,snehakachroo1/LSI_replica,grahamb/canvas-lms,jay3126/canvas-lms,sdeleon28/canvas-lms,arrivu/hoodemo,samuels410/greatlakes-lms,efrj/canvas-lms,usmschuck/canvas,sdeleon28/canvas-lms,utkarshx/canvas-lms,va7map/canvas-lms,grahamb/canvas-lms,matematikk-mooc/canvas-lms,usmschuck/canvas,venturehive/canvas-lms,samuels410/greatlakes-lms,wimemx/Canvas,AndranikMarkosyan/lms,merichar/canvas-lms,instructure/canvas-lms,landonwilkins/canvas-lms,wye0220/shindig-canvas,SwinburneOnline/canvas-lms,kyroskoh/canvas-lms,grahamb/canvas-lms,fronteerio/canvas-lms,matematikk-mooc/canvas-lms,utkarshx/canvas-lms,parbros/red-innovadores-lms,rup/Tarrax,grahamb/canvas-lms,landonwilkins/canvas-lms,venturehive/canvas-lms,snehakachroo1/LSI_replica,Rvor/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,tgroshon/canvas-lms,shidao-fm/canvas-lms,arrivu/hoodemo,wye0220/shindig-canvas,Unow/ins,arrivu/arrivu-lms,Rvor/canvas-lms,arrivu/hoodemo,ankithbti/canvas_lms,fronteerio/canvas-lms,Jyaasa/canvas-lms,greyhwndz/canvas-lms,djbender/canvas-lms,juoni/canvas-lms,Jyaasa/canvas-lms,sdeleon28/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,wimemx/Canvas,arrivu/qibla-ecampus,antoniuslin/canvas-lms,HotChalk/canvas-lms,roxolan/canvas-lms,sli7246/canvas_branch,nditech/red-innovadores-lms,shidao-fm/canvas-lms,shidao-fm/canvas-lms,arrivu/arrivu-lms,arrivu/hiring-site,kyroskoh/canvas-lms,ShreniiNepal/shrenii_lmp,landonwilkins/canvas-lms,djbender/canvas-lms,juoni/canvas-lms,SwinburneOnline/canvas-lms,matematikk-mooc/canvas-lms,va7map/canvas-lms,djbender/canvas-lms,nditech/red-innovadores-lms,va7map/canvas-lms,sli7246/canvas_branch,icelab/canvas,wrdsb/canvas-lms,kyroskoh/canvas-lms,loganrun/pincan,instructure/canvas-lms,tgroshon/canvas-lms,grahamb/canvas-lms,wrdsb/canvas-lms,redconfetti/canvas-lms,dgynn/canvas-lms,SwinburneOnline/canvas-lms,shidao-fm/canvas-lms,wimemx/Canvas,Unow/ins,juoni/canvas-lms,eCNAP/CANVAS,dgynn/canvas-lms,leftplusrightllc/canvas-lms,arrivu/arrivu-lms,HotChalk/canvas-lms,narigone/canvas,Unow/ins,whalejasmine/canvas-lms,eCNAP/CANVAS,antoniuslin/canvas-lms,utkarshx/canvas-lms,antoniuslin/canvas-lms,sfu/canvas-lms,icelab/canvas,arrivu/hiring-site,narigone/canvas,greyhwndz/canvas-lms,redconfetti/canvas-lms,Jyaasa/canvas-lms,AndranikMarkosyan/lms,wye0220/shindig-canvas,efrj/canvas-lms,ShreniiNepal/shrenii_lmp,snehakachroo1/LSI_replica,skmezanul/canvas-lms,loganrun/pincan,whalejasmine/canvas-lms,gbleydon/canvas-lms,dgynn/canvas-lms,jay3126/canvas-lms,arrivu/qibla-ecampus,parbros/red-innovadores-lms,Jyaasa/canvas-lms,gbleydon/canvas-lms,roxolan/canvas-lms,utkarshx/canvas-lms,jay3126/canvas-lms,skmezanul/canvas-lms,wrdsb/canvas-lms,parbros/red-innovadores-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,whalejasmine/canvas-lms,snehakachroo1/LSI_replica,samuels410/greatlakes-lms,Unow/canvas-lms,eCNAP/CANVAS,AndranikMarkosyan/lms,ankithbti/canvas_lms,HotChalk/canvas-lms,efrj/canvas-lms,tgroshon/canvas-lms,ShreniiNepal/shrenii_lmp,redconfetti/canvas-lms,instructure/canvas-lms,gbleydon/canvas-lms,Rvor/canvas-lms,instructure/canvas-lms,jay3126/canvas-lms,arrivu/jigsaw-lms,instructure/canvas-lms,rup/Tarrax,va7map/canvas-lms,instructure/canvas-lms,landonwilkins/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,roxolan/canvas-lms,ankithbti/canvas_lms,venturehive/canvas-lms,tgroshon/canvas-lms,greyhwndz/canvas-lms,matematikk-mooc/canvas-lms,leftplusrightllc/canvas-lms,arrivu/jigsaw-lms,skmezanul/canvas-lms,AndranikMarkosyan/lms,merichar/canvas-lms,arrivu/jigsaw-lms,juoni/canvas-lms,wrdsb/canvas-lms,kyroskoh/canvas-lms,usmschuck/canvas,djbender/canvas-lms,loganrun/pincan,skmezanul/canvas-lms,narigone/canvas,sli7246/canvas_branch,Unow/canvas-lms,efrj/canvas-lms,fronteerio/canvas-lms,leftplusrightllc/canvas-lms,instructure/canvas-lms,nditech/red-innovadores-lms,sdeleon28/canvas-lms,eCNAP/CANVAS,usmschuck/canvas,Unow/canvas-lms,Rvor/canvas-lms,merichar/canvas-lms,arrivu/qibla-ecampus,sfu/canvas-lms,ShreniiNepal/shrenii_lmp