Fix file descriptor and memory leak in autotools plugin

Don't create QFile's on heap when not needed.
Don't forget to delete those which have to created on heap.

Change-Id: I0e23e0d926febbfd464b3ff5d3e29fd46c16cb44
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>
Reviewed-by: Peter Penz <peter.penz19@gmail.com>