Check_MK Werk 7227: Fixed liveproxy activating errors confusing site related web API calls

ID: 7227 Title: Fixed liveproxy activating errors confusing site related web API calls Component: WATO Level: 1 Class: Bug fix Version: 1.6.0i1 Unclean error handling could make site management related web API calls like set_all_sites fail because an ASCII error message was sent back as result to the API call instead of the expected JSON data structure.