Make Pants goal run for Python exit with error code 1 if the python
program exits non-zero (as pants goal run does for java).

Testing Done:
Ran new tests.

Reviewed at https://rbcommons.com/s/twitter/r/1374/
Sync of https://github.com/pantsbuild/pants/commit/4399efcb2f0a7353b99be4872540c8043fc3c657