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. The notification worker does not actually need to use the value contained in the notification_id attribute of the ReloadUserInfoEvent. But it might be useful when debugging.