Bug 22709: Unit tests

Bug 22709: Unit tests

This patch introduces tests for new plugin hooks added to
C4::Biblio::{Add|Mod|Del}Biblio and C4::Items::{Add|Mod|Del}Item.

They are tested together as for creating an item you need to first create
a biblio and tests looks basically the same.

The testing strategy is
- Make sure the plugin is passed the right params
- Throw an exception at plugin-level, to be trapped by the C4::Biblio
and C4::Items lib, and converted into a warning. So we test for the
warning.
- Also, the fact that C4::Biblio and C4::Items warns, means the
exception was cought, and then Koha won't break on faulty plugins or
fatal errors from plugins.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>