This removes dependency to httplib2 by using urllib.
https://docs.python.org/3/library/http.client.html#httpresponse-objects

Use six for both py2/py3 unittest.

Bug: b/177465438
Change-Id: I48383559842615f97abea45b55ca0acf4d7c8bd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2629087
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@google.com>
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>