Bug 12031: (QA followup) adding supportdir to koha-conf.xml

Bug 12031: (QA followup) adding supportdir to koha-conf.xml

By adding a supportdir, this allows for configuring use in a
non-package install environment, such as git.

Seeing as I only tested git, I clearly had this defined.
Further testing should include packaging up an installation, and
installing a package version without setting the supportdir
configuration value.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>