Quiet does not silence functions with subprocess calls

[TheWizier]

For instance, apbs_surface with quiet = True does not silence the executable run with subprocess.call. This can be fixed by using:

import os
import subprocess

retcode = subprocess.call(['echo', 'foo'],
    stdout=subprocess.DEVNULL,
    stderr=subprocess.STDOUT)

ideally the output from the executable should be printed on the current process' stdout so that users can redirect it using redirect_stdout