use correct url on Windows platform

os.path.normpath is used to clean url. On windows platform, it
returns url with "\" instead of "/", which is required in heat api
 in:
/heat/heat/api/middleware/version_negotiation.py,
path_info_peek method.

Change-Id: Ic1a5fc5dd789a7996e08a85a9d8908267e203565
Closes-Bug: 1254657
Merge "use correct url on Windows platform"