Bug 18900: (QA followup) Make tests conditional to locale existence

Bug 18900: (QA followup) Make tests conditional to locale existence

It is important to highlight that tests have been skipped instead of having them pass
on the absence of the required fr_FR.UTF-8 locale installed on the system.

This patch does that check and effectively skips them.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 61f2ec769073709be3b688654ec355b3f4fbe522)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>