kiji-schema: SCHEMA-740. Start MiniZKCluster on a random port for ZooKeeper tests

issue: https://jira.kiji.org/browse/SCHEMA-740
review: https://review.kiji.org/r/1771
commit: https://github.com/kijiproject/kiji-schema/commit/4766a69f177d6b848f750f5869ccdda652f37f24