kiji-mapreduce: KIJIMR-292. Cassandra integration tests should use available ports (see CMP-2)

issue: https://jira.kiji.org/browse/KIJIMR-292
review: https://review.kiji.org/r/2044
commit: https://github.com/kijiproject/kiji-mapreduce/commit/80456fc0f6e48069fd54fc3debedbc206f5718f8