ipatest: loginscreen: do not use hardcoded password
Use admin password obtained from local config instead of hardcoded
value, as the password may differ in different testing environments.
https://pagure.io/freeipa/issue/9226
Signed-off-by: Michal Polovka <mpolovka@redhat.com>
Reviewed-By: Erik Belko <ebelko@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>