Checkmk Werk 10378: Improve "Update DNS cache" / cmk --update-dns-cache performance

ID: 10378 Title: Improve "Update DNS cache" / cmk --update-dns-cache performance Component: Core & setup Level: 1 Class: Bug fix Version: 1.7.0i1 The operation was performing a lot of needless operations. The update of several thousands of hosts DNS entries took way too long. The exact time needed depends mostly on the number of hosts, cache size, DNS lookup performance and so on. But even with good responding servers the operation took too long, because the cache was updated in a very inefficient way when calling the "Update DNS cache" action in WATO or "cmk --update-dns-cache" from the command line. The operation is now more than a 100 times faster (tested with ~2000 hosts and a fast responding DNS server).