Zxx Workstations need to use silent.bat instead of update.bat for ME updates

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To start the ME update, HP uses CallInst.exe which calls update.bat that performs the update. This batch file is normally silent and will run silently.

However, all Zxx Workstations will ask the user if it's OK to update the ME. As CallInst.exe runs the batch hidden, the operator has no chance to respond to this query and the update will run forever.

For a silent ME update, the batch silent.bat has to be used.

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Changed with commit a408650, closing issue.