Fix test runner to exit correctly.
Fix test runner to exit correctly.

The attempt at catching ImportError-driven exits seemed broken, so nuked it. Bah.

amaniak/fabric,elijah513/fabric,tekapo/fabric,mathiasertl/fabric,qinrong/fabric,SamuelMarks/fabric,tolbkni/fabric,rodrigc/fabric,sdelements/fabric,MjAbuz/fabric,TarasRudnyk/fabric,jaraco/fabric,pgroudas/fabric,xLegoz/fabric,getsentry/fabric,opavader/fabric,cgvarela/fabric,bitmonk/fabric,fernandezcuesta/fabric,rbramwell/fabric,likesxuqiang/fabric,hrubi/fabric,StackStorm/fabric,rane-hs/fabric-py3,raimon49/fabric,askulkarni2/fabric,pashinin/fabric,kxxoling/fabric,kmonsoor/fabric,cmattoon/fabric,haridsv/fabric,bspink/fabric,ploxiln/fabric,itoed/fabric,bitprophet/fabric