Bug 13791: make koha-list aware of plack

Bug 13791: make koha-list aware of plack

This patch adds the --plack and --noplack option switches to koha-list
for filtering instances to be listed.

This is particularly important for init scripts and cronjobs.

To test:
- Play with koha-list --plack and koha-plack --enable/--disable and verify that
koha-list returns the expected results.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>