kiji-mapreduce: KIJIMR-235. Unhelpful error messages for missformated --output

issue: https://jira.kiji.org/browse/KIJIMR-235
review: https://review.kiji.org/r/1600
commit: https://github.com/kijiproject/kiji-mapreduce/commit/265d0773ce8d22be17e03695d9e6f7c2c5a64519