Bug 18548: Print usage when missing instance name in koha-create script

Bug 18548: Print usage when missing instance name in koha-create script

Test plan:
1. Run: debian/scripts/koha-create --request-db
-> Without patch you see the getent error message
-> With patch you see usage and "Missing instance name" message

Signed-off-by: Dilan Johnpulle <dilan@calyx.net.au>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit d2ed4fadc59260372baedab038d16bd7cb169b1c)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>