Fix a very bad login bug.
Fix a very bad login bug.

We expected that paramiko would only ever throw AuthenticationExceptions upon
login failures, however, for standard password logins, some versions of
paramiko will throw an SSHException.

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