kiji-mapreduce: KIJIMR-296. Cassandra KijiMR integration tests should use only a single node

issue: https://jira.kiji.org/browse/KIJIMR-296
review: https://review.kiji.org/r/2081
commit: https://github.com/kijiproject/kiji-mapreduce/commit/80834beff7bcd85e8d3f47c7af963a3f727e88ce