With python3.x, classes can use 'metaclass=' instead of
'six.add_metaclass', 'six.iteritems' and 'six.iterkeys' can
be replaced by 'items' and 'keys', 'six.moves.urllib.parse'
can be replaced by 'urllib.parse', 'six.StringIO' and
'six.moves.cStringIO' can be replaced by 'io.StringIO',
'six.text_type' and 'six.string_type' are just 'str'.
Change-Id: I357968c6a1932856b1600f6c191966bc90cbc258
3cfa54fa56