Bug 27857: Regression tests

Bug 27857: Regression tests

This patch adds regression tests for the changed behavior.
Koha::Patron->extended_attributes will now throw exceptions and rollback
on invalid attributes.

The existing tests are amended so they don't try to deal with skipping
bad attributes.

Specific subtests are added for error situations.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Patron.t
=> FAIL: Tests fail because the new behavior is not implemented.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>