Test `config.py` crashes with commands that have no arguments

[karkhaz]

The config.py script used as a test in the CBMC starter kit crashes when the starter kit includes a Litani job whose command has no arguments.

The crash is on line 80 of config.py:

cmd, args = job['command'].strip().split(maxsplit=1)

A job's command is not guaranteed to have arguments, so the split can fail.