Check_MK Werk 6431: Fixed bulk discovery (addition to #6377 in 1.5.0)

ID: 6431 Title: Fixed bulk discovery (addition to #6377 in 1.5.0) Component: WATO Level: 1 Class: Bug fix Version: 1.6.0i1 The bulk discovery should've been fixed in 1.5.0 by werk #6377 which did not completely repair that feature. The error message "The selected element is not longer availalable" was shown when trying to do a bulk discovery.