allow Cluster.refresh_nodes to force token rebuild
allow Cluster.refresh_nodes to force token rebuild

PYTHON-349

stef1927/python-driver,stef1927/python-driver,coldeasy/python-driver,mambocab/python-driver,datastax/python-driver,thelastpickle/python-driver,vipjml/python-driver,coldeasy/python-driver,datastax/python-driver,vipjml/python-driver,mambocab/python-driver,thelastpickle/python-driver