webui-ci: fix table widget add
    
    add_table_record call used old selector for add button which
    caused 3 fails in CI:
    - ERROR: Test automember rebuild membership feature for hosts
    - ERROR: Test automember rebuild membership feature for users
    - ERROR: Basic CRUD: dns
    
    related to:
    https://fedorahosted.org/freeipa/ticket/4258
    
    Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>