swc-installation-test-2.py: Don't override Popen's 'close_fds'

Or 'shell'.  The support for these options can be flaky, and the
defaults change with Python version depending on what is best
supported [1].

[1]: http://docs.python.org/2/library/subprocess.html#subprocess.Popen

Reported-by: Ethan White <ethan@weecology.org>