Checkmk Werk 11784: mpre check missing handling for 'U' value in Nagios performance data

ID: 11784 Title: mpre check missing handling for 'U' value in Nagios performance data Component: Checks & agents Level: 1 Class: Bug fix Version: 2.1.0i1 Because the value 'U' (for undefined) has not been handled an exception gets thrown when processing such a value: ValueError (could not convert string to float: 'U') This change will just ignore undefined performance values.