[4/4] (Try8) msi/tests: Fix package test when run on a different drive than C:\.

[Nicolas Le Cam]

Try8: Change number of tries, as suggested by James. This patch was
already submitted in a previous patch set which was half accepted. Also
attach the correct patch.
Try7: Use helper function added in second patch, as suggested by James.

This one finally fixes current relative path test to expect correct
value.

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Nicolas Le Cam