Add unit tests for nailgun keystone middleware

- test for validating urls and methods that are not marked as public
- test for skipping validation of urls and methods marked as public
- fixed issue with args passed to exception raised when there is a problem with
  url regexp
- test for returning 401 in fake keystone middleware

Change-Id: I8f1215ee12b9931f6197e656c182753e8af5438d
Implements: blueprint access-control-master-node
Merge "Add unit tests for nailgun keystone middleware"