Check and delete for policy_association_for_region_and_service

Calls proper function in the manager and driver

Unit tests now check pre- and post- conditions on CRUD

Change-Id: I26e4d4f15ff39dd76141aa5fb7aae1ebb6680bf7
Closes-bug: 1400362
Merge "Check and delete for policy_association_for_region_and_service"