journald: Map the PRIORITY field to CIM_RecordForLog.PerceivedSeverity
    
    Records in journal may contain syslog-style priority value so let's use
    them. Unfortunately mapping the particular values between syslog and CIM
    classes is not linear, manual mapping is needed.
    
    The LOG_ERR may also map to PerceivedSeverity = Major but it's kept on
    Minor for the moment.
    
    If no such information is provided by the Journal, the CIM property is
    left unset for the particular record.
    
    See e.g. http://schemas.dmtf.org/wbem/cim-html/2.34.0/CIM_RecordForLog.html
    for valuemap description.