'XenPrep' corrections
'XenPrep' corrections

- Uncomment functions in DriverHandler.SystemClean()
- Correct spelling of 'xenevtchn'
- Change order of hwIDs in 'DriverHandler.CleanUpDrivers()';
  (better to remove root devices last)

Signed-off-by: Kostas Ladopoulos <7920ee5edb7fd3a4c6c6e3ebe9bd13d4a7f2eff1@citrix.com>

OwenSmith/win-installer,kostaslamda/win-installer,xenserver/win-installer,kostaslamda/win-installer,kostaslamda/win-installer,benchalmers/win-installer,benchalmers/win-installer,OwenSmith/win-installer,kostaslamda/win-installer,OwenSmith/win-installer,kostaslamda/win-installer,benchalmers/win-installer,xenserver/win-installer,benchalmers/win-installer,OwenSmith/win-installer,xenserver/win-installer,xenserver/win-installer,xenserver/win-installer,benchalmers/win-installer,OwenSmith/win-installer