Bug 16622: some tests triggered by prove t fail for unset KOHA_CONF

Bug 16622: some tests triggered by prove t fail for unset KOHA_CONF

TEST PLAN
---------
1) unset KOHA_CONF
2) prove t
   -- 00-load.t dies miserably
3) prove t/Creators.t
   -- fails
4) apply patch
5) prove t
   -- noisy, but all tests successful
6) prove -v t/Creators.t
   -- 2 skipped tests
7) run koha qa test tools

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>