Bug 16864: Silence warnings in t/db_dependent/ILSDI_Services.t

Bug 16864: Silence warnings in t/db_dependent/ILSDI_Services.t

prove t/db_dependent/ILSDI_Services.t
generates noisy output as a result of the ambiguous context
of two $cgi->param() calls.

By storing into scalar variables, and then using the scalar
variables, the code maintains readability and fixes the problem.

TEST PLAN
---------
1) prove t/db_dependent/ILSDI_Services.t
   -- noisy.
2) apply patch
3) prove t/db_dependent/ILSDI_Services.t
   -- not noisy
4) run koha qa test tools

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