There were some special cases in which the failed-service-logging policy
script might log a service being removed that was not removed due to an
analyzer violation. This change should fix these cases.
This commit renames the `service_violation` column that can be added via
a policy script to `failed_service`. This expresses the intent of it
better - the column contains services that failed and were removed after
confirmation.
Furthermore, the script is fixed so it actually does this - before it
would sometimes add services to the list that were not actually removed.
In the course of this, the type of the column was changed from a vector
to an ordered set.
Due to the column rename, the policy script itself is also renamed.
Also adds a NEWS entry for the DPD changes.
