Correct NetKAN staging metadata parser

[techman83]

Currently

method _build_staging {
  return $self->_raw->{config}{'x-netkan-staging'} ? $self->_raw->{config}{'x-netkan-staging'} : 0 ;
}

Should be

method _build_staging {
  return $self->_raw->{config}{'x_netkan_staging'} ? $self->_raw->{config}{'x_netkan_staging'} : 0 ;
}