Checkmk Werk 15426: check_mk_agent: fixing command when determining mrpe configured interval

ID: 15426 Title: check_mk_agent: fixing command when determining mrpe configured interval Component: agents Level: 1 Class: Bug fix Version: 2.3.0b1 Under certain OS, the -o flag of the grep command is unsupported and therefore led to a crash when attempting to determine the interval for the mrpe command. This werk fixes this issue.