Bug 6516 - Make borrowernumber of staff user configurable in koha-create

Bug 6516 - Make borrowernumber of staff user configurable in koha-create

Sets the default borrowernumber of staff user to 1 and makes it possible
to override this with ADMINUSER in /etc/koha/koha-sites.conf or with the
--adminuser and -a command line options.

Remember to update the wiki if this gets pushed!

Signed-off-by: Robin Sheat <robin@catalyst.net.nz>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit 8d8d2e6b441415724e667af95fefd9b0ea9c1bbc)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>