Update install-cassandra - set PasswordAuthenticator

Note that to create users and grant permissions, you need to have PasswordAuthenticator and CassandraAuthorizer enabled. I was using it to set up Datomic on Cassandra cluster. 
(you can read about what I was doing with it here: http://juliangamble.com/blog/2014/06/15/installing-cassandra-on-os-x-mavericks-using-docker-on-vagrant/)