Refactor test script check-ezid.py

[jsjiang]

Running test script check-ezid reported following error:

ezidapp.models.identifier.DoesNotExist: RefIdentifier matching query does not exist

Review the code to make sure records created for testing are all deleted accordingly and in the right order. For example, delete the records from the queues first, then from the refidentifier table, and last from the identifier table.