Checkmk Werk 13170: check_dns: added option to use default DNS server

ID: 13170 Title: check_dns: added option to use default DNS server Component: Checks & agents Level: 1 Class: New feature Version: 2.1.0i1 If no DNS server is specified the error message "CRITICAL - Plugin timed out while executing system call" could have been reported. The reason for this error is that the check_dns option "-s" is used with the hostname as DNS server. The host might not be a DNS server and a timeout occurs. The new option "Use default DNS server" will omit the option "-s" for check_dns. In this case the default DNS server of the checkmk server will be used and no timeout occurs any more.