Bug 10683: (follow-up) improvements to the unit tests

Bug 10683: (follow-up) improvements to the unit tests

The borrowers table needs to be cleared after the items table
(last_returned_by column).

Some checks were missing for GetRenewCount and AddRenewal.

Now the tests simulated a renewal for a item and check that the renews
left is decremented.

Moreover the issuingrules tables should be cleared and filled with known
values.

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