EXP-451. Express flow steps dont always start on YARN

Revamp express.py
 - Drop dependency on python-base:
   - use argparse
   - copy logging setup from python-base
 - Normalize classpath entries:
   - Normalize to absolute real paths (no symlinks)
   - Remove duplicates (by path name)
   - Remove classpath entries that do not exist
 - Add unit-tests for classpath normalization.

issue: https://jira.kiji.org/browse/EXP-451
review: https://review.kiji.org/r/2038