Bug 19049: Testing RecordsFromMarcPlugin with a to_marc plugin

Bug 19049: Testing RecordsFromMarcPlugin with a to_marc plugin

This patch adds a simple to_marc plugin in t/Koha/Plugin that is used
in the added subtest in ImportBatch.t.

Test plan:
[1] Run t/db_dependent/ImportBatch.t
[2] Copy the to_marc test plugin from t to your plugin directory.
    Under Debian packages, you should do something like:
    mkdir -p /var/lib/koha/master/plugins/Koha/Plugin/
    cp [yourclone]/t/Koha/Plugin/MarcFieldValues.pm /var/lib/koha/master/plugins/Koha/Plugin/
[3] Check if you see this plugin on plugins/plugins-home.pl
[4] Create a text file with some fields like:
    (Note: The plugin needs an empty line between both "records".)
    100,a = Test Author 1
    245,a = Title One

    100,a = Author 2
    245,a = Title Two
[5] Go to stage-marc-import.pl. Upload the created file. Select the plugin
    in the format combo and proceed. Did you create two records ?

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 83f60adbab8e96f0f14ec547029582623ac3a068)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>