QtIFW

Fixed writing log on Windows if target dir requires admin rights

Writing the installation log would fail on Windows in case writing to
the target directory requires admin privileges.

Instead of relying on the VerboseWriter destructor, let the
PackageManagerCore destructor explicitly write the installation log. In
case using the PlainVerboseWriterOutput does not work, try to use a
newly introduced VerboseWriterAdminOutput which first tries to acquire
admin privileges before writing a file via RemoteFileEngine.

Change-Id: I13f203afa67175012409bc1eed95f05e51cdcb81
Reviewed-by: Katja Marttila <katja.marttila@theqtcompany.com>