Werk #3070: windows agent: replaced a very costy section regarding installed software

To retrieve the list of installed software the mk_inventory.vbs script uses two different approaches that heavily overlap: One retrieves the list of uninstall-entries from the registry, the other retrieved the list of installers registered in the windows installer database (via wmi query to Win32_Product). The latter list is usually a subset of the former and can take excessively long to query as it triggers a verification of the database. In the process it also prints a lot of messages to the event log (see https://support.microsoft.com/de-de/kb/974524).

Therefore the query to Win32_Product has been replaced with a query via a vbs-interface to the installer database. This should produce the same results without the drawbacks mentioned.

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