urllib.urlopen() has issues with proxies similar to the ones reported in bug
134165 that are not present in urllib2.urlopen() -- namely, it does not
perform HTTP tunneling with proxy servers when fetching HTTPS URLs.

TEST=Pass --url=https://someurl to trychange.py behind a corporate proxy
R=maruel@chromium.org,iannucci@chromium.org,dpranke@chromium.org
BUG=

Review URL: https://codereview.chromium.org/133933007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@247914 0039d316-1c4b-4281-b951-d872f2087c98