This is similar to r247914 and r149742: urllib does not work with SSL
connections behind proxies, we need to use urllib2 instead. Doing this
should allow people behind proxies to download gsutils 4.7 after
r293413.

(Setting NOTRY here to be able to land the issue, otherwise the CQ fails when running some presubmit checks, see crbug.com/443232)

R=maruel@chromium.org, hinoka@chromium.org, pgervais@chromium.org, primiano@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/809053002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@293439 0039d316-1c4b-4281-b951-d872f2087c98