ipatests: webui: Use safe-loader for loading YAML configuration file
    
    FullLoader class for YAML loader was introduced in version 5.1 which
    also deprecated default loader. SafeLoader, however, stays consistent
    across the versions and brings added security.
    
    This fix is necessary as PyYAML > 5.1 is not available in downstream.
    
    Related: https://pagure.io/freeipa/issue/9009
    
    Signed-off-by: Michal Polovka <mpolovka@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>