upload example not python3

[Carl Karsten]

https://github.com/openstack/python-swiftclient/blob/master/examples/upload.py

Does not run in python 3:

```
$ python3 upload.py
Traceback (most recent call last):
  File "upload.py", line 3, in <module>
    from os.path import join, walk
ImportError: cannot import name 'walk'
```

ps -
I don't think upload.py is a good example. most of the code is about walking dirs and munging lists of python strings.
I think the whole upload.py should be thrown out and replaced with something that just uploads a static list of files.

This is much closer to what I want, if only it started with the imports.
https://github.com/openstack/python-swiftclient/blob/master/doc/source/client-api.rst
 "Create a new object with the contents of a local text file:"