Reduce repetitive invocations of QFINDTESTDATA.

Store the file names in variables instead.

Task-number: QTBUG-38890
Change-Id: I65f28bb62674f14aa099e935a9d7a4e9e6e90ba9
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>