Part of OOIION-654

* Added the method, get_subscriptions_for_user() for UNS.

This method takes the user-id as an input parameter. The logic will first find all notification requests for this resource then if a user_id is present, it will filter on those that this user is associated with.

Added a test for the this method. The test method is called: test_get_subscriptions_for_user()
Checked different scenarios in the test to see that the method works.

* Fixed the update method which was not publishing the ReloadUserInfo event with the notification id passed in as a parameter. Fixed the test, test_pub_reload_user_info_event(), which checks that the create, update and delete notification methods correctly send the ReloadUserInfo which is used by the notification workers to reload their user info dicts.