Introduce QFINDTESTDATA and set the current directory
of the process to the test directory such that it works
indepently of the working directory of executable location.

Change-Id: I8105ba0fa7d9da7ff920d10f3a083433e2590e9f
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Honglei Zhang <honglei.zhang@nokia.com>