Fix the remainder of the API usage tests. Note that this still fails when the blueprint is registered again, so each subset of tests has to be run on its own

endpoints/common.py

@@ -74,7 +74,7 @@ def common_login(db_user):
 @app.errorhandler(model.DataModelException)
 def handle_dme(ex):
   logger.exception(ex)
-  return make_response(ex.message, 400)
+  return make_response(json.dumps({'message': ex.message}), 400)
 
 
 def generate_csrf_token():