Fix path() method implementation and adding SWIFT_EXTRA_OPTIONS

By default, swiftclient.get_auth always returns publicURL when using keystone with OpenStack swift implementation. Adding extra options to swiftclient.get_auth fix this kind of operation. Also, according with django File system storage API:

```
For storage systems that aren’t accessible from the local filesystem, this will raise NotImplementedError instead.
```
So, I've rename path() method and returns NotImplementedError with original path() method