Bug 31614: Adds a koha-conf.xml config to set Zebra connection timeout

Bug 31614: Adds a koha-conf.xml config to set Zebra connection timeout

This patch adds <zebra_connection_timeout>30</zebra_connection_timeout>
to the koha-conf.xml file.

Sometimes, a Zebra search might take longer than 30 seconds. If it does,
Koha will say that 0 records have been found. While slow searching
is not desirable, it's more desirable to get the result set regardless.

Test plan:
0. Apply patch
1. Add <zebra_connection_timeout>.1</zebra_connection_timeout> to
your relevant koha-conf.xml file (e.g. /etc/koha/sites/kohadev/koha-conf.xml)
2. echo 'flush_all' | nc -q 1 memcached 11211
3. koha-plack --restart kohadev
4. Go to http://localhost:8081/cgi-bin/koha/catalogue/search.pl?q=test
5. Note that no results are returned
6. Change zebra_connection_timeout to 30
7. echo 'flush_all' | nc -q 1 memcached 11211
8. koha-plack --restart kohadev
9a. Go to http://localhost:8081/cgi-bin/koha/catalogue/search.pl?q=test
9b. Note that 3 results are returned
10. Remove zebra_connection_timeout from koha-conf.xml
11. echo 'flush_all' | nc -q 1 memcached 11211
12. koha-plack --restart kohadev
13a. Go to http://localhost:8081/cgi-bin/koha/catalogue/search.pl?q=test
13b. Note that 3 results are returned
14. Celebrate

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>