Adding a periodic task to remove zombie proxy users

Changes
* adding periodic task for user removal
* adding a wrapper function for the periodic tasks class to improve
  configuration
* refactoring proxy user delete function to allow a user id

Change-Id: I641e1650e7a5fcd96246e13b7e1d548c4a0dda25
Partial-implements: blueprint edp-swift-trust-authentication
Merge "Adding a periodic task to remove zombie proxy users"