kiji-express: EXP-429. Differentiate express.sh and express.py

issue: https://jira.kiji.org/browse/EXP-429
review: https://review.kiji.org/r/1763
commit: https://github.com/kijiproject/kiji-express/commit/a94183b9fb893b9152fafb6597a77c0559f2c8e7