Bug 17932: (followup) Tidy tests

Bug 17932: (followup) Tidy tests

This patch makes the tests create its own data instead of searching the
DB for a branchcode and a categorycode. It does so on each subtest,
because there shouldn't be side effects between subtests.

I also wrapped each subtest inside a transaction, for the same reason.

To test:
- Apply this patch
- Run:
  $ prove t/db_dependent/Koha/Object.t
=> SUCCESS: Tests return green with this patch
- Sign off :-D

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>