Use six.moves.http_client instead of httplib

The httplib module has been renamed to http.client in Python 3.
We can use six.moves.http_client to let it support Python 3.
See http://docs.python.org/2/library/httplib.html#module-httplib

Part of blueprint py33

Change-Id: I860446d808b182852edad205f4e0cde586a864aa
Merge "Use six.moves.http_client instead of httplib"