*Possible* fix for #2318.  Not sure if this will fix @cdeil's specific issue, but it *did* fix the issue for me running on my laptop on the institute network.
Disable use of proxy servers by urllib2 entirely when internet is disabled
Fix the proxy-disable to work on Python 2/3
Merge pull request #2318 from embray/issue-2318

IOError from unit tests in disable_internet.py in localhost check