Bug 15323: Use fixtures for the active currency

 Bug 15323: Use fixtures for the active currency

  prove t/Prices.t
fails after bug 15084 has been pushed
It's caused by
  commit 1538e9ecf47642c4974693ff499c3e95e4d71977
    Bug 15084: Replace C4::Budgets::GetCurrencies with
    Koha::Acquisition::Currencies->search

Koha::Number::Price->_format_params calls
Koha::Acquisition::Currencies->get_active, which requests the DB.
The currency data should be mocked.

Test plan:
sudo service mysql stop
prove t/Prices.t
 should return green

Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>
Patch works as expected and passes the qa-tools tests.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>