Port FileLikeIter and _MultipartMimeFileLikeObject and
swift.common.utils to Python 3:
* Add a __next__() alias to the next() method. On Python 3, the
next() method is no more used, __next__() is required.
* Use literal byte strings: FileLikeIter _MultipartMimeFileLikeObject
are written to handle binary files.
* test_close(): replace .FileLikeIter('abcdef') with
FileLikeIter([b'a', b'b', b'c']). On Python 3, list(b'abc') returns
[97, 98, 99], whereas ['a', 'b', 'c'] is returned on Python 2.
* Update unit FileLikeIter tests to use byte strings.
Change-Id: Ibacddb70b22f624ecd83e374749578feddf8bca8
6c32da14f4