Bug 14685: Fix set guarantor for a child or professional accounts

Bug 14685: Fix set guarantor for a child or professional accounts

Bug 13970 removed some useful code to automatically set the guarantor
when creating a child.

But finally there is a better way to do the job, we just need to assume
that only children or professional can have a guarantor.

Test plan:
1/ Create an adult patron and add a child.
2/ The guarantor info should be retrieved and set on the child creation
page.
3/ Create an organization and add a child
4/ The guarantor info should be retrieved and set on the adult creation
page.

Signed-off-by: Liz Rea <liz@catalyst.net.nz>
This patch catches both cases, thanks Jonathan!

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>