kiji-mapreduce: KIJIMR-289.  Add Cassandra support to KijiMR.

review: https://review.kiji.org/r/1971
issue: https://jira.kiji.org/KIJIMR-289
commit: https://github.com/kijiproject/kiji-mapreduce/commit/0283466ab6b0919715adeaab636b2f705a9a5446