Fixed flaw in unit tests so they can be reliably parallelized.
Fixed flaw in unit tests so they can be reliably parallelized.

Fixed a bug which made parallelizing the unit tests with pytest-xdist unreliable.

The unit tests can now be run in parallel using pytest-xdist for a dramatic speedup on multicore machines.  To do this use:
    py.test -n4
(where 4 is the number of cores you wish to parallelize across)

python-cmd2/cmd2,python-cmd2/cmd2