Bug 17777: koha-remove should deal with temporary uploads

Bug 17777: koha-remove should deal with temporary uploads

If the temporary upload folder exists, it should be discarded when
removing an instance. If we do not, it may/will create problems when
recreating the same instance.

A function in koha-functions.sh is added to determine the temp directory
instead of hardcoding /tmp.

Test plan:
[1] Copy koha-functions.sh to /usr/share/koha/bin
[2] Run koha-create --create-db newinstancexx
[3] Run mkdir /tmp/koha_newinstancexx_upload (if /tmp is your temp!)
[4] Run debian/scripts/koha-remove newinstancexx
    Do not run the regular one, but verify that you use the updated one.
[5] Check that /tmp/koha_newinstancexx_upload is gone.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Karen Jen <karenliang.student@wegc.school.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>