Make sure the outputDirectory contains the full path not relative.

Trying to run a process using the relative path on windows fails.

Task-number: QTBUG-41431
Change-Id: I0c9aa837dc7a556372b1018feb2f7f5c14c2652a
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>