OmeroPy: Fix path handling and renaming for Python 2.7 on Windows

Update path.py to work with Python 2.7 on Windows, and also fix the ConfigXML rewriting which was also broken and prevented running the cli.

Testing: Should make bin/omero work with Python 2.7 / Ice 3.5 on Windows. And there should be no regressions on any existing supported platform: ensure all python code such as dropbox is still functional.

--rebased-from #2356