Checkmk Werk 13910: Fix wrong start and end time for downtimes

ID: 13910 Title: Fix wrong start and end time for downtimes Component: Core & setup Level: 1 Class: Bug fix Version: 2.2.0i1 This fixes a regression introduced in 2.1 where the start time and the end time of the downtimes were computed incorrectly. This could result in a shift of several hours, depending on the local time of the server.