Catch correct oslo.db exception

Now oslo.db wraps all the database exceptions into specific oslo.db
exceptions. A test expects for IntegrityError where now returns
DBDuplicateEntry. We should catch DBDuplicateEntry to keep test
correctness.

Change-Id: I4576f19c4fd3db6742a6a2fbbca0e0e5400b792d
Closes-Bug: #1214341
Merge "Catch correct oslo.db exception"