Make import tests more resilient to race condition failures
Make import tests more resilient to race condition failures

Also centralises wait-or-assert logic.
Drezi126/osu,smoogipooo/osu,2yangk23/osu,peppy/osu,ZLima12/osu,ppy/osu,ZLima12/osu,EVAST9919/osu,DrabWeb/osu,smoogipoo/osu,naoey/osu,naoey/osu,smoogipoo/osu,peppy/osu,Nabile-Rahmani/osu,UselessToucan/osu,DrabWeb/osu,johnneijzen/osu,smoogipoo/osu,peppy/osu-new,2yangk23/osu,NeoAdonis/osu,ppy/osu,NeoAdonis/osu,peppy/osu,Frontear/osuKyzer,EVAST9919/osu,NeoAdonis/osu,UselessToucan/osu,ppy/osu,UselessToucan/osu,johnneijzen/osu,DrabWeb/osu,naoey/osu