Correctly set final exception when query fails on all hosts
Correctly set final exception when query fails on all hosts

Before this change, the Event that notifies listeners
that the operation has completed was not being triggered.

coldeasy/python-driver,tempbottle/python-driver,stef1927/python-driver,thelastpickle/python-driver,yi719/python-driver,kracekumar/python-driver,HackerEarth/cassandra-python-driver,datastax/python-driver,sontek/python-driver,datastax/python-driver,kishkaru/python-driver,markflorisson/python-driver,kishkaru/python-driver,vipjml/python-driver,bbirand/python-driver,mambocab/python-driver,mambocab/python-driver,mike-tr-adamson/python-driver,yi719/python-driver,markflorisson/python-driver,jfelectron/python-driver,mobify/python-driver,thobbs/python-driver,vipjml/python-driver,mobify/python-driver,thelastpickle/python-driver,bbirand/python-driver,thobbs/python-driver,jfelectron/python-driver,jregovic/python-driver,jregovic/python-driver,sontek/python-driver,beobal/python-driver,kracekumar/python-driver,tempbottle/python-driver,stef1927/python-driver,beobal/python-driver,coldeasy/python-driver,mike-tr-adamson/python-driver,HackerEarth/cassandra-python-driver