Allow anonymous access to the discovery endpoint

Fixes https://jira.coreos.com/browse/QS-101

endpoints/api/discovery.py

@@ -12,6 +12,7 @@ from app import app
 from auth import scopes
 from endpoints.api import (ApiResource, resource, method_metadata, nickname, truthy_bool,
                            parse_args, query_param)
+from endpoints.decorators import anon_allowed
 
 
 logger = logging.getLogger(__name__)
@@ -326,6 +327,7 @@ class DiscoveryResource(ApiResource):
   @parse_args()
   @query_param('internal', 'Whether to include internal APIs.', type=truthy_bool, default=False)
   @nickname('discovery')
+  @anon_allowed
   def get(self, parsed_args):
     """ List all of the API endpoints available in the swagger API format."""
     return swagger_route_data(parsed_args['internal'])