Allow keystoneclient to work with older keystone installs

Older keystone installs may return 501 for GET / instead of 300
like today. We should be able to assume that if 501 is returned the
server will support v2.0 only.

Fixes bug 1159911

Change-Id: If264840d8678a490264f1bdb62f1b51c362619e1

keystoneclient/middleware/auth_token.py

@@ -410,7 +410,10 @@ class AuthProtocol(object):
     def _get_supported_versions(self):
         versions = []
         response, data = self._json_request('GET', '/')
-        if response.status != 300:
+        if response.status == 501:
+            self.LOG.warning("Old keystone installation found...assuming v2.0")
+            versions.append("v2.0")
+        elif response.status != 300:
             self.LOG.error('Unable to get version info from keystone: %s' %
                            response.status)
             raise ServiceError('Unable to get version info from keystone')