Bug 28234: TestBuilder->build_sample_biblio should set UTF-8 encoding for record

Bug 28234: TestBuilder->build_sample_biblio should set UTF-8 encoding for record

This patch makes the build_sample_biblio method, correctly set the UTF-8
flag for the MARC::Record object.

Tests are added.

To test:
1. Apply the regression tests patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/TestBuilder.t
FAIL: Tests fail! An unexpected encoding warning shows
3. Apply this patch
4. Repeat 2
=> SUCCESS: No warning! Tests pass!
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>