Change tests to accommodate pg differences.

**Test Only**

I propose that we amend the import error tests to check:

* That at least one error was returned.
* That it is of the type DataImportError.
 
At that point we should be relatively confident that import errors are being handled in a sane way.  Getting this test to pass will get us back to a build where Postgres passes regularly and we can go back to tracking down the intermittent failures.

Refs #2499
- Since PostgreSQL handles transactions differently than
  MySQL and SQLite3 there are differences in the way and
  number of errors that are returned.  Update tests to
  only check that at least one error of the proper type
  was returned.