Bug 13928: Clean up noisy t/Borrower.t tests

Bug 13928: Clean up noisy t/Borrower.t tests

While testing bug 13882, noisy messages were noticed. Also,
Test::Warn was used, but no catching attempts were made. This
patch solves that problem.

TEST PLAN
---------
1) prove -v t/Borrowers.t
   -- There should be three noisy lines.
2) apply patch
3) prove -v t/Borrowers.t
   -- There will be 3 more tests and no noisy lines.
4) Run koha qa test tool
   -- There should be no issues.

NOTE: This will conflict with bug 13882 if either gets pushed
      to master, but fixing the conflict should be easy enough.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Works as expected

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>