Bug 29025: Don't prefill userid and password in user creation form

Bug 29025: Don't prefill userid and password in user creation form

Recent Firefox versions try to prefill userid and password with
logged in user credentials.

To test
1 - Log in staff as user foo password bar
2 - Save user and password in Firefox
3 - Log out
4 - Log in again, log in pop-up must be pre-filled
5 - Open Create a new patron form
6 - At least password field is pre-filled with logged in user's credentials
7 - Apply patch
8 - Redo 4 and 5
9 - Userid and password fields aren't prefilled

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>