kiji-express: EXP-325. KIJI_CLASSPATH should be used in classpath to express shell.

issue: https://jira.kiji.org/browse/EXP-325
review: https://review.kiji.org/r/1586
commit: https://github.com/kijiproject/kiji-express/commit/22c15604a35775f090fc3522c77d428c440ebac8