Bug 10332: further improvements to course reserves tests

Bug 10332: further improvements to course reserves tests

- Wrap tests in a database transaction; that
  way, no special cleanup code is required
- Use AddItem rather than AddItemFromMarc to create
  test items; there's no need to build in a
  dependence on any particular MARC flavor or
  framework in our test cases (except, of course,
  for test cases that are explicitly exercising
  code that involves the frameworks).

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>