Bug 21111: Add --exclude-indexes to koha-run-backups

Bug 21111: Add --exclude-indexes to koha-run-backups

This patch adds a trivial switch so koha-run-backups can pass the
--exclude-indexes option switch to koha-dump. This way if the sysadmin
doesn't want to backup the Zebra indexes, it can be controlled by
tweaking the cron definition.

To test:
1. Apply this patch
2. Run:
   $ debian/scripts/koha-run-backups --days 2 --output /var/spool/koha
3. Notice the size of the backups:
   $ ls -lh /var/spool/koha/kohadev
4. Try the new option switch:
   $ debian/scripts/koha-run-backups \
       --exclude-indexes \
       --days 2 --output /var/spool/koha
5. Repeat 3
=> SUCCESS: Backups are smaller!
6. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
JD amended patch: fix --exclude_indexes vs --exclude-indexes in koha-run-backups.xml

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>