Checkmk Werk 12343: fix missing __id in folders after upgrade from 1.6.0

ID: 12343 Title: fix missing __id in folders after upgrade from 1.6.0 Component: Core & setup Level: 1 Class: Bug fix Version: 2.1.0i1 When upgrading from 1.6.0 to 2.0.0 until 2.0.0p3, only the root-folder got assigned a __id key which is required for the folder endpoints of the REST API. Access to other folders with the REST API would result in a HTTP 500 error with an error message. During the upgrade to 2.0.0p4, these folders will be fixed. No further action (apart from upgrading) is necessary.