NMS-4763: Add WMI Terminal Service session metrics for Win2K8

- Renamed existing WMI group for Windows 2003 Server from win32_terminalservices to win32_terminalservices2003
- Added new WMI group for Windows 2008 with win32_terminalservices2008 which provides terminal service metrics in a new WMI class Win32_PerfFormattedData_TermService_TerminalServices