Comment 3 for bug 843457

Fix proposed with lp:~cgb-cs/appscale/tools-with-zero-db-detection - the ips.yaml above has only a single database node, which means it gets assigned as db_master. The tools were only checking for database nodes (of which db_master is not), so it counted a total of zero database nodes (since database means db_slave) and thus assigned replication = 0, which caused the unavailable exception thrown by Cassandra.

Fix committed causes tools to die if they detect zero database nodes and properly counts database masters as database nodes.