Bug 15714: Add get_loglevels to koha-functions.sh

Bug 15714: Add get_loglevels to koha-functions.sh

Preparing for including different log levels in koha-start-zebra.
Note that the default response is none,fatal,warn; this is equal
to the options passed to zebrasrv in koha-start-zebra (for now).

Test plan:
[1] Run on the command line: source koha-functions.sh
[2] Type get_loglevels [your_instance]
    By default, you should see: none,fatal,warn
[3] Add this line to your koha-conf:
    <zebra_loglevels>how,are,you</zebra_loglevels>
[4] Run get_loglevels [your_instance] again.
    Remove the nonsense log levels again..

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com