Fix sabre directory test cases
Fix sabre directory test cases

- rely on a mock subfolder instead of the root
- remove obsolete "Shared" limitation tests which did pass but not for the right
  reasons
- added test for the prevention of root deletion

jbicha/server,IljaN/core,xx621998xx/server,Ardinis/server,endsguy/server,andreas-p/nextcloud-server,IljaN/core,IljaN/core,owncloud/core,endsguy/server,nextcloud/server,pollopolea/core,bluelml/core,andreas-p/nextcloud-server,pmattern/server,pmattern/server,jbicha/server,owncloud/core,jbicha/server,michaelletzgus/nextcloud-server,pixelipo/server,sharidas/core,pollopolea/core,sharidas/core,andreas-p/nextcloud-server,cernbox/core,IljaN/core,sharidas/core,bluelml/core,pollopolea/core,pollopolea/core,whitekiba/server,lrytz/core,pmattern/server,pmattern/server,whitekiba/server,Ardinis/server,owncloud/core,xx621998xx/server,pixelipo/server,jbicha/server,cernbox/core,cernbox/core,lrytz/core,endsguy/server,pixelipo/server,lrytz/core,whitekiba/server,pollopolea/core,nextcloud/server,sharidas/core,owncloud/core,phil-davis/core,whitekiba/server,whitekiba/server,michaelletzgus/nextcloud-server,sharidas/core,xx621998xx/server,endsguy/server,cernbox/core,jbicha/server,Ardinis/server,michaelletzgus/nextcloud-server,andreas-p/nextcloud-server,IljaN/core,owncloud/core,pixelipo/server,Ardinis/server,nextcloud/server,Ardinis/server,michaelletzgus/nextcloud-server,lrytz/core,bluelml/core,pixelipo/server,pmattern/server,endsguy/server,andreas-p/nextcloud-server,cernbox/core,xx621998xx/server,bluelml/core,lrytz/core,xx621998xx/server,bluelml/core,nextcloud/server