SMARTS Leaves Behind Zombie Processes

[Gamenot]

SMARTS is orphaning processes leaving behind a number of orphaned process ids. We will need to clean these up so that long-running and distributed training will be successful.

It looks like it has more relation to the heterogeneous agent computing changes.

Example command line signature of the zombie processes:
python smarts/zoo/run_agent.py --socket_file /tmp/tmpXXXX --auth_key

See: #295 (comment) for the example of how to reproduce this problem.

AC:

• SMARTS does not create zombie processes during run
• Address to connection closed by SUMO #295 (comment) on if solving this problem also solved 295.