kiji-model-repository: KIJIREPO-56. Cleanup test resource leaks

issue: https://jira.kiji.org/browse/KIJIREPO-56
review: https://review.kiji.org/r/1863
commit: https://github.com/kijiproject/kiji-model-repository/commit/5b3063bc589e03d971bb4e3936dcbbf1eef022da