let standardclient cache regionless auth1 tokens

When an auth1 url is given with no `auth_region` and `cache_auth` is enabled then swiftly bombs out like this in _auth_save_cache because region is None. Letting it become '' like the other non-essential fields lets it save fine.

      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/swiftly/client/standardclient.py", line 160, in _auth_save_cache
        self.cdn_url or '', self.auth_token, str(self.snet)])
    TypeError: sequence item 4: expected string, NoneType found