1f10aeb ipatest: loginscreen: do not use hardcoded password

Authored and Committed by mpolovka a year ago
    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>