refactor a conditional for testing and understanding
refactor a conditional for testing and understanding

_cleanup_running_deleted_instances was getting
difficult to understand, so I extracted a method
that contained the calculation about what is to be
deleted. Also, added tests for that method.

update: _shutdown_instance has an arity of three,
the existing code gives four arguments, one was
passed through to driver.destroy, which now has a
default argument that defaults to True, the passed
value.

update 2: Doh! pep8

Change-Id: I1a32512a4e0d80ba4dcc911b96790c29c1f36710
n0ano/ganttclient